diff --git a/test/fixtures/wpt/README.md b/test/fixtures/wpt/README.md
index 096c876f7b2956..855fca6d179ff6 100644
--- a/test/fixtures/wpt/README.md
+++ b/test/fixtures/wpt/README.md
@@ -12,9 +12,9 @@ Last update:
 
 - console: https://github.com/web-platform-tests/wpt/tree/3b1f72e99a/console
 - encoding: https://github.com/web-platform-tests/wpt/tree/1821fb5f77/encoding
-- url: https://github.com/web-platform-tests/wpt/tree/54c6d64be0/url
-- resources: https://github.com/web-platform-tests/wpt/tree/1d14e821b9/resources
-- interfaces: https://github.com/web-platform-tests/wpt/tree/15e47f779c/interfaces
+- url: https://github.com/web-platform-tests/wpt/tree/09d8830be1/url
+- resources: https://github.com/web-platform-tests/wpt/tree/001e50de41/resources
+- interfaces: https://github.com/web-platform-tests/wpt/tree/8719553b2d/interfaces
 - html/webappapis/microtask-queuing: https://github.com/web-platform-tests/wpt/tree/2c5c3c4c27/html/webappapis/microtask-queuing
 - html/webappapis/timers: https://github.com/web-platform-tests/wpt/tree/264f12bc7b/html/webappapis/timers
 - hr-time: https://github.com/web-platform-tests/wpt/tree/a5d1774ecf/hr-time
diff --git a/test/fixtures/wpt/interfaces/html.idl b/test/fixtures/wpt/interfaces/html.idl
index e92bb8690dddd3..bf8da3733ec26f 100644
--- a/test/fixtures/wpt/interfaces/html.idl
+++ b/test/fixtures/wpt/interfaces/html.idl
@@ -436,7 +436,6 @@ interface HTMLIFrameElement : HTMLElement {
   [SameObject, PutForwards=value] readonly attribute DOMTokenList sandbox;
   [CEReactions] attribute DOMString allow;
   [CEReactions] attribute boolean allowFullscreen;
-  [CEReactions] attribute boolean allowPaymentRequest;
   [CEReactions] attribute DOMString width;
   [CEReactions] attribute DOMString height;
   [CEReactions] attribute DOMString referrerPolicy;
@@ -1564,16 +1563,18 @@ dictionary ElementDefinitionOptions {
 
 [Exposed=Window]
 interface ElementInternals {
-  // Form-associated custom elements
+  // Shadow root access
+  readonly attribute ShadowRoot? shadowRoot;
 
+  // Form-associated custom elements
   undefined setFormValue((File or USVString or FormData)? value,
-                    optional (File or USVString or FormData)? state);
+                         optional (File or USVString or FormData)? state);
 
   readonly attribute HTMLFormElement? form;
 
   undefined setValidity(optional ValidityStateFlags flags = {},
-                   optional DOMString message,
-                   optional HTMLElement anchor);
+                        optional DOMString message,
+                        optional HTMLElement anchor);
   readonly attribute boolean willValidate;
   readonly attribute ValidityState validity;
   readonly attribute DOMString validationMessage;
@@ -1583,6 +1584,9 @@ interface ElementInternals {
   readonly attribute NodeList labels;
 };
 
+// Accessibility semantics
+ElementInternals includes ARIAMixin;
+
 dictionary ValidityStateFlags {
   boolean valueMissing = false;
   boolean typeMismatch = false;
@@ -2353,6 +2357,18 @@ interface WorkerLocation {
   readonly attribute USVString hash;
 };
 
+[Exposed=Worklet, SecureContext]
+interface WorkletGlobalScope {};
+
+[Exposed=Window, SecureContext]
+interface Worklet {
+  [NewObject] Promise<undefined> addModule(USVString moduleURL, optional WorkletOptions options = {});
+};
+
+dictionary WorkletOptions {
+  RequestCredentials credentials = "same-origin";
+};
+
 [Exposed=Window]
 interface Storage {
   readonly attribute unsigned long length;
diff --git a/test/fixtures/wpt/resources/test-only-api.m.js b/test/fixtures/wpt/resources/test-only-api.m.js
new file mode 100644
index 00000000000000..984f635abac002
--- /dev/null
+++ b/test/fixtures/wpt/resources/test-only-api.m.js
@@ -0,0 +1,5 @@
+/* Whether the browser is Chromium-based with MojoJS enabled */
+export const isChromiumBased = 'MojoInterfaceInterceptor' in self;
+
+/* Whether the browser is WebKit-based with internal test-only API enabled */
+export const isWebKitBased = !isChromiumBased && 'internals' in self;
diff --git a/test/fixtures/wpt/resources/test-only-api.m.js.headers b/test/fixtures/wpt/resources/test-only-api.m.js.headers
new file mode 100644
index 00000000000000..5e8f640c6659d1
--- /dev/null
+++ b/test/fixtures/wpt/resources/test-only-api.m.js.headers
@@ -0,0 +1,2 @@
+Content-Type: text/javascript; charset=utf-8
+Cache-Control: max-age=3600
diff --git a/test/fixtures/wpt/resources/testdriver-actions.js b/test/fixtures/wpt/resources/testdriver-actions.js
index 870a2e8e266780..f3e6388e8acd19 100644
--- a/test/fixtures/wpt/resources/testdriver-actions.js
+++ b/test/fixtures/wpt/resources/testdriver-actions.js
@@ -9,6 +9,7 @@
   function Actions(defaultTickDuration=16) {
     this.sourceTypes = new Map([["key", KeySource],
                                 ["pointer", PointerSource],
+                                ["wheel", WheelSource],
                                 ["none", GeneralSource]]);
     this.sources = new Map();
     this.sourceOrder = [];
@@ -22,6 +23,7 @@
     this.createSource("none");
     this.tickIdx = 0;
     this.defaultTickDuration = defaultTickDuration;
+    this.context = null;
   }
 
   Actions.prototype = {
@@ -65,7 +67,17 @@
       } catch(e) {
         return Promise.reject(e);
       }
-      return test_driver.action_sequence(actions);
+      return test_driver.action_sequence(actions, this.context);
+    },
+
+    /**
+     * Set the context for the actions
+     *
+     * @param {WindowProxy} context - Context in which to run the action sequence
+     */
+    setContext: function(context) {
+      this.context = context;
+      return this;
     },
 
     /**
@@ -73,7 +85,7 @@
      * If no name is passed, a new source with the given type is
      * created.
      *
-     * @param {String} type - Source type ('none', 'key', or 'pointer')
+     * @param {String} type - Source type ('none', 'key', 'pointer', or 'wheel')
      * @param {String?} name - Name of the source
      * @returns {Source} Source object for that source.
      */
@@ -154,6 +166,32 @@
       return this;
     },
 
+    /**
+     * Add a new wheel input source with the given name
+     *
+     * @param {String} type - Name of the wheel source
+     * @param {Bool} set - Set source as the default wheel source
+     * @returns {Actions}
+     */
+    addWheel: function(name, set=true) {
+      this.createSource("wheel", name);
+      if (set) {
+        this.setWheel(name);
+      }
+      return this;
+    },
+
+    /**
+     * Set the current default wheel source
+     *
+     * @param {String} name - Name of the wheel source
+     * @returns {Actions}
+     */
+    setWheel: function(name) {
+      this.setSource("wheel", name);
+      return this;
+    },
+
     createSource: function(type, name, parameters={}) {
       if (!this.sources.has(type)) {
         throw new Error(`${type} is not a valid action type`);
@@ -196,8 +234,9 @@
      *
      * @param {Number?} duration - Minimum length of the tick in ms.
      * @param {String} sourceType - source type
-     * @param {String?} sourceName - Named key or pointer source to use or null for the default
-     *                               key or pointer source
+     * @param {String?} sourceName - Named key, pointer or wheel source to use
+     *                               or null for the default key, pointer or
+     *                               wheel source
      * @returns {Actions}
      */
     pause: function(duration=0, sourceType="none", {sourceName=null}={}) {
@@ -280,6 +319,27 @@
       source.pointerMove(this, x, y, duration, origin);
       return this;
     },
+
+    /**
+     * Create a scroll event for the current default wheel source
+     *
+     * @param {Number} x - mouse cursor x coordinate
+     * @param {Number} y - mouse cursor y coordinate
+     * @param {Number} deltaX - scroll delta value along the x-axis in pixels
+     * @param {Number} deltaY - scroll delta value along the y-axis in pixels
+     * @param {String|Element} origin - Origin of the coordinate system.
+     *                                  Either "viewport" or an Element
+     * @param {Number?} duration - Time in ms for the scroll
+     * @param {String?} sourceName - Named wheel source to use or null for the
+     *                               default wheel source
+     * @returns {Actions}
+     */
+    scroll: function(x, y, deltaX, deltaY,
+                     {origin="viewport", duration, sourceName=null}={}) {
+      let source = this.getSource("wheel", sourceName);
+      source.scroll(this, x, y, deltaX, deltaY, duration, origin);
+      return this;
+    },
   };
 
   function GeneralSource() {
@@ -417,5 +477,46 @@
     },
   };
 
+  function WheelSource() {
+    this.actions = new Map();
+  }
+
+  WheelSource.prototype = {
+    serialize: function(tickCount) {
+      if (!this.actions.size) {
+        return undefined;
+      }
+      let actions = [];
+      let data = {"type": "wheel", "actions": actions};
+      for (let i=0; i<tickCount; i++) {
+        if (this.actions.has(i)) {
+          actions.push(this.actions.get(i));
+        } else {
+          actions.push({"type": "pause"});
+        }
+      }
+      return data;
+    },
+
+    scroll: function(actions, x, y, deltaX, deltaY, duration, origin) {
+      let tick = actions.tickIdx;
+      if (this.actions.has(tick)) {
+        tick = actions.addTick().tickIdx;
+      }
+      this.actions.set(tick, {type: "scroll", x, y, deltaX, deltaY, origin});
+      if (duration) {
+        this.actions.get(tick).duration = duration;
+      }
+    },
+
+    addPause: function(actions, duration) {
+      let tick = actions.tickIdx;
+      if (this.actions.has(tick)) {
+        tick = actions.addTick().tickIdx;
+      }
+      this.actions.set(tick, {type: "pause", duration: duration});
+    },
+  };
+
   test_driver.Actions = Actions;
 })();
diff --git a/test/fixtures/wpt/resources/testdriver.js b/test/fixtures/wpt/resources/testdriver.js
index 4d373c9281d85e..c53b24136c091f 100644
--- a/test/fixtures/wpt/resources/testdriver.js
+++ b/test/fixtures/wpt/resources/testdriver.js
@@ -1,6 +1,7 @@
 (function() {
     "use strict";
     var idCounter = 0;
+    let testharness_context = null;
 
     function getInViewCenterPoint(rect) {
         var left = Math.max(0, rect.left);
@@ -15,7 +16,8 @@
     }
 
     function getPointerInteractablePaintTree(element) {
-        if (!window.document.contains(element)) {
+        let elementDocument = element.ownerDocument;
+        if (!elementDocument.contains(element)) {
             return [];
         }
 
@@ -27,10 +29,10 @@
 
         var centerPoint = getInViewCenterPoint(rectangles[0]);
 
-        if ("elementsFromPoint" in document) {
-            return document.elementsFromPoint(centerPoint[0], centerPoint[1]);
-        } else if ("msElementsFromPoint" in document) {
-            var rv = document.msElementsFromPoint(centerPoint[0], centerPoint[1]);
+        if ("elementsFromPoint" in elementDocument) {
+            return elementDocument.elementsFromPoint(centerPoint[0], centerPoint[1]);
+        } else if ("msElementsFromPoint" in elementDocument) {
+            var rv = elementDocument.msElementsFromPoint(centerPoint[0], centerPoint[1]);
             return Array.prototype.slice.call(rv ? rv : []);
         } else {
             throw new Error("document.elementsFromPoint unsupported");
@@ -47,6 +49,31 @@
      * @namespace
      */
     window.test_driver = {
+        /**
+         * Set the context in which testharness.js is loaded
+         *
+         * @param {WindowProxy} context - the window containing testharness.js
+         **/
+        set_test_context: function(context) {
+          if (window.test_driver_internal.set_test_context) {
+            window.test_driver_internal.set_test_context(context);
+          }
+          testharness_context = context;
+        },
+
+        /**
+         * postMessage to the context containing testharness.js
+         *
+         * @param {Object} msg - the data to POST
+         **/
+        message_test: function(msg) {
+            let target = testharness_context;
+            if (testharness_context === null) {
+                target = window;
+            }
+            target.postMessage(msg, "*");
+        },
+
         /**
          * Trigger user interaction in order to grant additional privileges to
          * a provided function.
@@ -56,30 +83,35 @@
          * @param {String} intent - a description of the action which much be
          *                          triggered by user interaction
          * @param {Function} action - code requiring escalated privileges
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled following user interaction and
          *                    execution of the provided `action` function;
          *                    rejected if interaction fails or the provided
          *                    function throws an error
          */
-        bless: function(intent, action) {
-            var button = document.createElement("button");
+        bless: function(intent, action, context=null) {
+            let contextDocument = context ? context.document : document;
+            var button = contextDocument.createElement("button");
             button.innerHTML = "This test requires user interaction.<br />" +
                 "Please click here to allow " + intent + ".";
             button.id = "wpt-test-driver-bless-" + (idCounter += 1);
-            const elem = document.body || document.documentElement;
+            const elem = contextDocument.body || contextDocument.documentElement;
             elem.appendChild(button);
 
-            return new Promise(function(resolve, reject) {
-                    button.addEventListener("click", resolve);
+            let wait_click = new Promise(resolve => button.addEventListener("click", resolve));
 
-                    test_driver.click(button).catch(reject);
-                }).then(function() {
+            return test_driver.click(button)
+                .then(wait_click)
+                .then(function() {
                     button.remove();
 
                     if (typeof action === "function") {
                         return action();
                     }
+                    return null;
                 });
         },
 
@@ -95,14 +127,6 @@
          *                    the cases the WebDriver command errors
          */
         click: function(element) {
-            if (window.top !== window) {
-                return Promise.reject(new Error("can only click in top-level window"));
-            }
-
-            if (!window.document.contains(element)) {
-                return Promise.reject(new Error("element in different document or shadow tree"));
-            }
-
             if (!inView(element)) {
                 element.scrollIntoView({behavior: "instant",
                                         block: "end",
@@ -135,14 +159,6 @@
          *                    the cases the WebDriver command errors
          */
         send_keys: function(element, keys) {
-            if (window.top !== window) {
-                return Promise.reject(new Error("can only send keys in top-level window"));
-            }
-
-            if (!window.document.contains(element)) {
-                return Promise.reject(new Error("element in different document or shadow tree"));
-            }
-
             if (!inView(element)) {
                 element.scrollIntoView({behavior: "instant",
                                         block: "end",
@@ -166,34 +182,42 @@
          * https://github.com/WICG/page-lifecycle/blob/master/README.md|Lifecycle API
          * for Web Pages}
          *
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
+         *
          * @returns {Promise} fulfilled after the freeze request is sent, or rejected
          *                    in case the WebDriver command errors
          */
-        freeze: function() {
+        freeze: function(context=null) {
             return window.test_driver_internal.freeze();
         },
 
         /**
          * Send a sequence of actions
          *
-         * This function sends a sequence of actions to the top level window
+         * This function sends a sequence of actions
          * to perform. It is modeled after the behaviour of {@link
          * https://w3c.github.io/webdriver/#actions|WebDriver Actions Command}
          *
          * @param {Array} actions - an array of actions. The format is the same as the actions
-                                    property of the WebDriver command {@link
-                                    https://w3c.github.io/webdriver/#perform-actions|Perform
-                                    Actions} command. Each element is an object representing an
-                                    input source and each input source itself has an actions
-                                    property detailing the behaviour of that source at each timestep
-                                    (or tick). Authors are not expected to construct the actions
-                                    sequence by hand, but to use the builder api provided in
-                                    testdriver-actions.js
+         *                          property of the WebDriver command {@link
+         *                          https://w3c.github.io/webdriver/#perform-actions|Perform
+         *                          Actions} command. Each element is an object representing an
+         *                          input source and each input source itself has an actions
+         *                          property detailing the behaviour of that source at each timestep
+         *                          (or tick). Authors are not expected to construct the actions
+         *                          sequence by hand, but to use the builder api provided in
+         *                          testdriver-actions.js
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
+         *
          * @returns {Promise} fufiled after the actions are performed, or rejected in
          *                    the cases the WebDriver command errors
          */
-        action_sequence: function(actions) {
-            return window.test_driver_internal.action_sequence(actions);
+        action_sequence: function(actions, context=null) {
+            return window.test_driver_internal.action_sequence(actions, context);
         },
 
         /**
@@ -203,11 +227,15 @@
          * by ReportingObserver) for testing purposes, as described in
          * {@link https://w3c.github.io/reporting/#generate-test-report-command}
          *
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
+         *
          * @returns {Promise} fulfilled after the report is generated, or
          *                    rejected if the report generation fails
          */
-        generate_test_report: function(message) {
-            return window.test_driver_internal.generate_test_report(message);
+        generate_test_report: function(message, context=null) {
+            return window.test_driver_internal.generate_test_report(message, context);
         },
 
         /**
@@ -221,6 +249,9 @@
          *                              object
          * @param {String} state - the state of the permission
          * @param {boolean} one_realm - Optional. Whether the permission applies to only one realm
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * The above params are used to create a [PermissionSetParameters]{@link
          * https://w3c.github.io/permissions/#dictdef-permissionsetparameters} object
@@ -228,13 +259,13 @@
          * @returns {Promise} fulfilled after the permission is set, or rejected if setting the
          *                    permission fails
          */
-        set_permission: function(descriptor, state, one_realm) {
+        set_permission: function(descriptor, state, one_realm, context=null) {
             let permission_params = {
               descriptor,
               state,
               oneRealm: one_realm,
             };
-            return window.test_driver_internal.set_permission(permission_params);
+            return window.test_driver_internal.set_permission(permission_params, context);
         },
 
         /**
@@ -247,12 +278,16 @@
          * @param {Object} config - an [Authenticator Configuration]{@link
          *                          https://w3c.github.io/webauthn/#authenticator-configuration}
          *                          object
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
+         *
          * @returns {Promise} fulfilled after the authenticator is added, or
          *                    rejected in the cases the WebDriver command
          *                    errors. Returns the ID of the authenticator
          */
-        add_virtual_authenticator: function(config) {
-            return window.test_driver_internal.add_virtual_authenticator(config);
+        add_virtual_authenticator: function(config, context=null) {
+            return window.test_driver_internal.add_virtual_authenticator(config, context);
         },
 
         /**
@@ -264,13 +299,16 @@
          *
          * @param {String} authenticator_id - the ID of the authenticator to be
          *                                    removed.
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled after the authenticator is removed, or
          *                    rejected in the cases the WebDriver command
          *                    errors
          */
-        remove_virtual_authenticator: function(authenticator_id) {
-            return window.test_driver_internal.remove_virtual_authenticator(authenticator_id);
+        remove_virtual_authenticator: function(authenticator_id, context=null) {
+            return window.test_driver_internal.remove_virtual_authenticator(authenticator_id, context);
         },
 
         /**
@@ -282,13 +320,16 @@
          * @param {Object} credential - A [Credential Parameters]{@link
          *                              https://w3c.github.io/webauthn/#credential-parameters}
          *                              object
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled after the credential is added, or
          *                    rejected in the cases the WebDriver command
          *                    errors
          */
-        add_credential: function(authenticator_id, credential) {
-            return window.test_driver_internal.add_credential(authenticator_id, credential);
+        add_credential: function(authenticator_id, credential, context=null) {
+            return window.test_driver_internal.add_credential(authenticator_id, credential, context);
         },
 
         /**
@@ -300,6 +341,9 @@
          * https://w3c.github.io/webauthn/#sctn-automation-get-credentials
          *
          * @param {String} authenticator_id - the ID of the authenticator
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled after the credentials are returned, or
          *                    rejected in the cases the WebDriver command
@@ -307,8 +351,8 @@
          *                    Parameters]{@link
          *                    https://w3c.github.io/webauthn/#credential-parameters}
          */
-        get_credentials: function(authenticator_id) {
-            return window.test_driver_internal.get_credentials(authenticator_id);
+        get_credentials: function(authenticator_id, context=null) {
+            return window.test_driver_internal.get_credentials(authenticator_id, context=null);
         },
 
         /**
@@ -318,13 +362,16 @@
          *
          * @param {String} authenticator_id - the ID of the authenticator
          * @param {String} credential_id - the ID of the credential
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled after the credential is removed, or
          *                    rejected in the cases the WebDriver command
          *                    errors.
          */
-        remove_credential: function(authenticator_id, credential_id) {
-            return window.test_driver_internal.remove_credential(authenticator_id, credential_id);
+        remove_credential: function(authenticator_id, credential_id, context=null) {
+            return window.test_driver_internal.remove_credential(authenticator_id, credential_id, context);
         },
 
         /**
@@ -333,13 +380,16 @@
          * https://w3c.github.io/webauthn/#sctn-automation-remove-all-credentials
          *
          * @param {String} authenticator_id - the ID of the authenticator
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} fulfilled after the credentials are removed, or
          *                    rejected in the cases the WebDriver command
          *                    errors.
          */
-        remove_all_credentials: function(authenticator_id) {
-            return window.test_driver_internal.remove_all_credentials(authenticator_id);
+        remove_all_credentials: function(authenticator_id, context=null) {
+            return window.test_driver_internal.remove_all_credentials(authenticator_id, context);
         },
 
         /**
@@ -351,9 +401,12 @@
          *
          * @param {String} authenticator_id - the ID of the authenticator
          * @param {boolean} uv - the User Verified flag
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          */
-        set_user_verified: function(authenticator_id, uv) {
-            return window.test_driver_internal.set_user_verified(authenticator_id, uv);
+        set_user_verified: function(authenticator_id, uv, context=null) {
+            return window.test_driver_internal.set_user_verified(authenticator_id, uv, context);
         },
 
         /**
@@ -370,16 +423,19 @@
          *                                    May be "*" to indicate all origins.
          * @param {String} state - The storage access setting.
          *                         Must be either "allowed" or "blocked".
+         * @param {WindowProxy} context - Browsing context in which
+         *                                to run the call, or null for the current
+         *                                browsing context.
          *
          * @returns {Promise} Fulfilled after the storage access rule has been
          *                    set, or rejected if setting the rule fails.
          */
-        set_storage_access: function(origin, embedding_origin, state) {
+        set_storage_access: function(origin, embedding_origin, state, context=null) {
             if (state !== "allowed" && state !== "blocked") {
                 throw new Error("storage access status must be 'allowed' or 'blocked'");
             }
             const blocked = state === "blocked";
-            return window.test_driver_internal.set_storage_access(origin, embedding_origin, blocked);
+            return window.test_driver_internal.set_storage_access(origin, embedding_origin, blocked, context);
         },
     };
 
@@ -392,13 +448,6 @@
          */
         in_automation: false,
 
-        /**
-         * Waits for a user-initiated click
-         *
-         * @param {Element} element - element to be clicked
-         * @param {{x: number, y: number} coords - viewport coordinates to click at
-         * @returns {Promise} fulfilled after click occurs
-         */
         click: function(element, coords) {
             if (this.in_automation) {
                 return Promise.reject(new Error('Not implemented'));
@@ -409,14 +458,6 @@
             });
         },
 
-        /**
-         * Waits for an element to receive a series of key presses
-         *
-         * @param {Element} element - element which should receve key presses
-         * @param {String} keys - keys to expect
-         * @returns {Promise} fulfilled after keys are received or rejected if
-         *                    an incorrect key sequence is received
-         */
         send_keys: function(element, keys) {
             if (this.in_automation) {
                 return Promise.reject(new Error('Not implemented'));
@@ -449,158 +490,52 @@
             });
         },
 
-        /**
-         * Freeze the current page
-         *
-         * @returns {Promise} fulfilled after freeze request is sent, otherwise
-         * it gets rejected
-         */
-        freeze: function() {
+        freeze: function(context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Send a sequence of pointer actions
-         *
-         * @returns {Promise} fufilled after actions are sent, rejected if any actions
-         *                    fail
-         */
-        action_sequence: function(actions) {
+        action_sequence: function(actions, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Generates a test report on the current page
-         *
-         * @param {String} message - the message to be contained in the report
-         * @returns {Promise} fulfilled after the report is generated, or
-         *                    rejected if the report generation fails
-         */
-        generate_test_report: function(message) {
+        generate_test_report: function(message, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
 
-        /**
-         * Sets the state of a permission
-         *
-         * This function simulates a user setting a permission into a particular state as described
-         * in {@link https://w3c.github.io/permissions/#set-permission-command}
-         *
-         * @param {Object} permission_params - a [PermissionSetParameters]{@lint
-         *                                     https://w3c.github.io/permissions/#dictdef-permissionsetparameters}
-         *                                     object
-         * @returns {Promise} fulfilled after the permission is set, or rejected if setting the
-         *                    permission fails
-         */
-        set_permission: function(permission_params) {
+        set_permission: function(permission_params, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Creates a virtual authenticator
-         *
-         * @param {Object} config - the authenticator configuration
-         * @returns {Promise} fulfilled after the authenticator is added, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors.
-         */
-        add_virtual_authenticator: function(config) {
+        add_virtual_authenticator: function(config, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Removes a virtual authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator to be
-         *                                    removed.
-         *
-         * @returns {Promise} fulfilled after the authenticator is removed, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors
-         */
-        remove_virtual_authenticator: function(authenticator_id) {
+        remove_virtual_authenticator: function(authenticator_id, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Adds a credential to a virtual authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator
-         * @param {Object} credential - A [Credential Parameters]{@link
-         *                              https://w3c.github.io/webauthn/#credential-parameters}
-         *                              object
-         *
-         * @returns {Promise} fulfilled after the credential is added, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors
-         *
-         */
-        add_credential: function(authenticator_id, credential) {
+        add_credential: function(authenticator_id, credential, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Gets all the credentials stored in an authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator
-         *
-         * @returns {Promise} fulfilled after the credentials are returned, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors. Returns an array of [Credential
-         *                    Parameters]{@link
-         *                    https://w3c.github.io/webauthn/#credential-parameters}
-         *
-         */
-        get_credentials: function(authenticator_id) {
+        get_credentials: function(authenticator_id, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Remove a credential stored in an authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator
-         * @param {String} credential_id - the ID of the credential
-         *
-         * @returns {Promise} fulfilled after the credential is removed, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors.
-         *
-         */
-        remove_credential: function(authenticator_id, credential_id) {
+        remove_credential: function(authenticator_id, credential_id, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Removes all the credentials stored in a virtual authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator
-         *
-         * @returns {Promise} fulfilled after the credentials are removed, or
-         *                    rejected in the cases the WebDriver command
-         *                    errors.
-         *
-         */
-        remove_all_credentials: function(authenticator_id) {
+        remove_all_credentials: function(authenticator_id, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Sets the User Verified flag on an authenticator
-         *
-         * @param {String} authenticator_id - the ID of the authenticator
-         * @param {boolean} uv - the User Verified flag
-         *
-         */
-        set_user_verified: function(authenticator_id, uv) {
+        set_user_verified: function(authenticator_id, uv, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
 
-        /**
-         * Sets the storage access policy for a third-party origin when loaded
-         * in the current first party context
-         */
-        set_storage_access: function(origin, embedding_origin, blocked) {
+        set_storage_access: function(origin, embedding_origin, blocked, context=null) {
             return Promise.reject(new Error("unimplemented"));
         },
     };
diff --git a/test/fixtures/wpt/resources/testharness.js b/test/fixtures/wpt/resources/testharness.js
index 61eadfeb6541a9..d50e094117df56 100644
--- a/test/fixtures/wpt/resources/testharness.js
+++ b/test/fixtures/wpt/resources/testharness.js
@@ -520,6 +520,43 @@ policies and contribution forms [3].
             Object.prototype.toString.call(worker) == '[object ServiceWorker]';
     }
 
+    var seen_func_name = Object.create(null);
+
+    function get_test_name(func, name)
+    {
+        if (name) {
+            return name;
+        }
+
+        if (func) {
+            var func_code = func.toString();
+
+            // Try and match with brackets, but fallback to matching without
+            var arrow = func_code.match(/^\(\)\s*=>\s*(?:{(.*)}\s*|(.*))$/);
+
+            // Check for JS line separators
+            if (arrow !== null && !/[\u000A\u000D\u2028\u2029]/.test(func_code)) {
+                var trimmed = (arrow[1] !== undefined ? arrow[1] : arrow[2]).trim();
+                // drop trailing ; if there's no earlier ones
+                trimmed = trimmed.replace(/^([^;]*)(;\s*)+$/, "$1");
+
+                if (trimmed) {
+                    let name = trimmed;
+                    if (seen_func_name[trimmed]) {
+                        // This subtest name already exists, so add a suffix.
+                        name += " " + seen_func_name[trimmed];
+                    } else {
+                        seen_func_name[trimmed] = 0;
+                    }
+                    seen_func_name[trimmed] += 1;
+                    return name;
+                }
+            }
+        }
+
+        return test_environment.next_default_test_name();
+    }
+
     /*
      * API functions
      */
@@ -530,17 +567,18 @@ policies and contribution forms [3].
             tests.status.message = '`test` invoked after `promise_setup`';
             tests.complete();
         }
-        var test_name = name ? name : test_environment.next_default_test_name();
+        var test_name = get_test_name(func, name);
         var test_obj = new Test(test_name, properties);
         var value = test_obj.step(func, test_obj, test_obj);
 
         if (value !== undefined) {
-            var msg = "Test named \"" + test_name +
-                "\" inappropriately returned a value";
+            var msg = 'Test named "' + test_name +
+                '" passed a function to `test` that returned a value.';
 
             try {
-                if (value && value.hasOwnProperty("then")) {
-                    msg += ", consider using `promise_test` instead";
+                if (value && typeof value.then === 'function') {
+                    msg += ' Consider using `promise_test` instead when ' +
+                        'using Promises or async/await.';
                 }
             } catch (err) {}
 
@@ -565,10 +603,33 @@ policies and contribution forms [3].
             name = func;
             func = null;
         }
-        var test_name = name ? name : test_environment.next_default_test_name();
+        var test_name = get_test_name(func, name);
         var test_obj = new Test(test_name, properties);
         if (func) {
-            test_obj.step(func, test_obj, test_obj);
+            var value = test_obj.step(func, test_obj, test_obj);
+
+            // Test authors sometimes return values to async_test, expecting us
+            // to handle the value somehow. Make doing so a harness error to be
+            // clear this is invalid, and point authors to promise_test if it
+            // may be appropriate.
+            //
+            // Note that we only perform this check on the initial function
+            // passed to async_test, not on any later steps - we haven't seen a
+            // consistent problem with those (and it's harder to check).
+            if (value !== undefined) {
+                var msg = 'Test named "' + test_name +
+                    '" passed a function to `async_test` that returned a value.';
+
+                try {
+                    if (value && typeof value.then === 'function') {
+                        msg += ' Consider using `promise_test` instead when ' +
+                            'using Promises or async/await.';
+                    }
+                } catch (err) {}
+
+                tests.set_status(tests.status.ERROR, msg);
+                tests.complete();
+            }
         }
         return test_obj;
     }
@@ -579,7 +640,7 @@ policies and contribution forms [3].
             name = func;
             func = null;
         }
-        var test_name = name ? name : test_environment.next_default_test_name();
+        var test_name = get_test_name(func, name);
         var test = new Test(test_name, properties);
         test._is_promise_test = true;
 
@@ -1323,10 +1384,16 @@ policies and contribution forms [3].
                "expected a number but got a ${type_actual}",
                {type_actual:typeof actual});
 
-        assert(Math.abs(actual - expected) <= epsilon,
-               "assert_approx_equals", description,
-               "expected ${expected} +/- ${epsilon} but got ${actual}",
-               {expected:expected, actual:actual, epsilon:epsilon});
+        // The epsilon math below does not place nice with NaN and Infinity
+        // But in this case Infinity = Infinity and NaN = NaN
+        if (isFinite(actual) || isFinite(expected)) {
+            assert(Math.abs(actual - expected) <= epsilon,
+                   "assert_approx_equals", description,
+                   "expected ${expected} +/- ${epsilon} but got ${actual}",
+                   {expected:expected, actual:actual, epsilon:epsilon});
+        } else {
+            assert_equals(actual, expected);
+        }
     }
     expose(assert_approx_equals, "assert_approx_equals");
 
@@ -3773,7 +3840,7 @@ policies and contribution forms [3].
     function get_title()
     {
         if ('document' in global_scope) {
-            //Don't use document.title to work around an Opera bug in XHTML documents
+            //Don't use document.title to work around an Opera/Presto bug in XHTML documents
             var title = document.getElementsByTagName("title")[0];
             if (title && title.firstChild && title.firstChild.data) {
                 return title.firstChild.data;
diff --git a/test/fixtures/wpt/url/README.md b/test/fixtures/wpt/url/README.md
index 823a8eec022282..50a71bb482df9e 100644
--- a/test/fixtures/wpt/url/README.md
+++ b/test/fixtures/wpt/url/README.md
@@ -44,6 +44,10 @@ expected to fail.
 Tests in `/encoding` and `/html/infrastructure/urls/resolving-urls/query-encoding/` cover the
 encoding argument to the URL parser.
 
+There's also limited coverage in `resources/percent-encoding.json` for percent-encode after encoding
+with _percentEncodeSet_ set to special-query percent-encode set and _spaceAsPlus_ set to false.
+(Improvements to expand coverage here are welcome.)
+
 ## Specification
 
 The tests in this directory assert conformance with [the URL Standard][URL].
diff --git a/test/fixtures/wpt/url/percent-encoding.window.js b/test/fixtures/wpt/url/percent-encoding.window.js
new file mode 100644
index 00000000000000..dcb5c1e55b21b7
--- /dev/null
+++ b/test/fixtures/wpt/url/percent-encoding.window.js
@@ -0,0 +1,33 @@
+promise_test(() => fetch("resources/percent-encoding.json").then(res => res.json()).then(runTests), "Loading data…");
+
+function runTests(testUnits) {
+  for (const testUnit of testUnits) {
+    // Ignore comments
+    if (typeof testUnit === "string") {
+      continue;
+    }
+    for (const encoding of Object.keys(testUnit.output)) {
+      async_test(t => {
+        const frame = document.body.appendChild(document.createElement("iframe"));
+        t.add_cleanup(() => frame.remove());
+        frame.onload = t.step_func_done(() => {
+          const output = frame.contentDocument.querySelector("a");
+          // Test that the fragment is always UTF-8 encoded
+          assert_equals(output.hash, `#${testUnit.output["utf-8"]}`, "fragment");
+          assert_equals(output.search, `?${testUnit.output[encoding]}`, "query");
+        });
+        frame.src = `resources/percent-encoding.py?encoding=${encoding}&value=${toBase64(testUnit.input)}`;
+      }, `Input ${testUnit.input} with encoding ${encoding}`);
+    }
+  }
+}
+
+// Use base64 to avoid relying on the URL parser to get UTF-8 percent-encoding correctly. This does
+// not use btoa directly as that only works with code points in the range U+0000 to U+00FF,
+// inclusive.
+function toBase64(input) {
+  const bytes = new TextEncoder().encode(input);
+  const byteString = Array.from(bytes, byte => String.fromCharCode(byte)).join("");
+  const encoded = self.btoa(byteString);
+  return encoded;
+}
diff --git a/test/fixtures/wpt/url/resources/percent-encoding.json b/test/fixtures/wpt/url/resources/percent-encoding.json
new file mode 100644
index 00000000000000..eccd1db62fe601
--- /dev/null
+++ b/test/fixtures/wpt/url/resources/percent-encoding.json
@@ -0,0 +1,48 @@
+[
+  "Tests for percent-encoding.",
+  {
+    "input": "\u2020",
+    "output": {
+      "big5": "%26%238224%3B",
+      "euc-kr": "%A2%D3",
+      "utf-8": "%E2%80%A0",
+      "windows-1252": "%86"
+    }
+  },
+  "This uses a trailing A to prevent the URL parser from trimming the C0 control.",
+  {
+    "input": "\u000EA",
+    "output": {
+      "big5": "%0EA",
+      "iso-2022-jp": "%26%2365533%3BA",
+      "utf-8": "%0EA"
+    }
+  },
+  {
+    "input": "\u203E\u005C",
+    "output": {
+      "iso-2022-jp": "%1B(J~%1B(B\\",
+      "utf-8": "%E2%80%BE\\"
+    }
+  },
+  {
+    "input": "\uE5E5",
+    "output": {
+      "gb18030": "%26%2358853%3B",
+      "utf-8": "%EE%97%A5"
+    }
+  },
+  {
+    "input": "\u2212",
+    "output": {
+      "shift_jis": "%81|",
+      "utf-8": "%E2%88%92"
+    }
+  },
+  {
+    "input": "á|",
+    "output": {
+      "utf-8": "%C3%A1|"
+    }
+  }
+]
diff --git a/test/fixtures/wpt/versions.json b/test/fixtures/wpt/versions.json
index e18a5e0213fb3e..f1e9b8304d5fda 100644
--- a/test/fixtures/wpt/versions.json
+++ b/test/fixtures/wpt/versions.json
@@ -8,15 +8,15 @@
     "path": "encoding"
   },
   "url": {
-    "commit": "54c6d64be071c60baaad8c4da0365b962ffbe77c",
+    "commit": "09d8830be15da7e3a44f32a934609c25357d6ef3",
     "path": "url"
   },
   "resources": {
-    "commit": "1d14e821b9586f250e6a31d550504e3d16a05ae7",
+    "commit": "001e50de41dc35820774b27e31f77a165f4c0b9b",
     "path": "resources"
   },
   "interfaces": {
-    "commit": "15e47f779cf61555669b0f67e2c49b9c830b9019",
+    "commit": "8719553b2dd8f0f39d38253ccac2ee9ab4d6c87b",
     "path": "interfaces"
   },
   "html/webappapis/microtask-queuing": {
@@ -39,4 +39,4 @@
     "commit": "7caa3de7471cf19b78ee9efa313c7341a462b5e3",
     "path": "dom/abort"
   }
-}
+}
\ No newline at end of file
diff --git a/test/wpt/status/url.json b/test/wpt/status/url.json
index 9038f6df80703e..89601af0ca5814 100644
--- a/test/wpt/status/url.json
+++ b/test/wpt/status/url.json
@@ -3,6 +3,10 @@
     "requires": ["small-icu"],
     "skip": "TODO: port from .window.js"
   },
+  "percent-encoding.window.js": {
+    "requires": ["small-icu"],
+    "skip": "TODO: port from .window.js"
+  },
   "historical.any.js": {
     "requires": ["small-icu"]
   },