diff --git a/portals/portals-focus.sub.html b/portals/portals-focus.sub.html
index a05786186e5d332..1427dae2e4d13cd 100644
--- a/portals/portals-focus.sub.html
+++ b/portals/portals-focus.sub.html
@@ -1,6 +1,8 @@
 <!DOCTYPE html>
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
 <script src="resources/open-blank-host.js"></script>
 <body>
 <script>
@@ -14,59 +16,89 @@
 
   promise_test(async t => {
     let portal = await createPortal(document, new URL("resources/focus-page-with-button.html", location.href));
-    portal.onmessage = t.step_func(e => {
-      assert_unreached("button inside portal should not be focused");
-    });
-    portal.postMessage("focus", "*");
-    return new Promise(r => t.step_timeout(r, 500));
+    try {
+      portal.onmessage = t.step_func(e => {
+        assert_unreached("button inside portal should not be focused");
+      });
+      portal.postMessage("focus", "*");
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
   }, "test that an element inside a portal cannot steal focus");
 
   promise_test(async t => {
     let portal = await createPortal(document, new URL("resources/focus-page-with-x-origin-iframe.sub.html", location.href));
-    portal.onmessage = t.step_func(e => {
-      assert_unreached("button inside portal should not be focused");
-    });
-    portal.postMessage("focus", "*");
-    return new Promise(r => t.step_timeout(r, 500));
+    try {
+      portal.onmessage = t.step_func(e => {
+        assert_unreached("button inside portal should not be focused");
+      });
+      portal.postMessage("focus", "*");
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
   }, "test that an element inside a portal's x-origin subframe cannot steal focus");
 
   promise_test(async t => {
     let win = await openBlankPortalHost();
     let doc = win.document;
+    try {
+      let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
+      let button = doc.createElement("button");
+      doc.body.appendChild(button);
 
-    let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
-    let button = doc.createElement("button");
-    doc.body.appendChild(button);
+      await portal.activate();
+      doc.body.removeChild(portal);
 
-    await portal.activate();
-    doc.body.removeChild(portal);
-
-    button.onfocus = t.step_func(() => {
-      assert_unreached("button inside adopted portal should not be focused");
-    });
-    button.focus();
-    return new Promise(r => t.step_timeout(r, 500));
+      button.onfocus = t.step_func(() => {
+        assert_unreached("button inside adopted portal should not be focused");
+      });
+      button.focus();
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      win.close();
+    }
   }, "test that an element inside an adopted portal cannot steal focus");
 
   promise_test(async t => {
     let win = await openBlankPortalHost();
     let doc = win.document;
+    try {
+      let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
+      let iframe = doc.createElement("iframe");
+      iframe.src = new URL("resources/focus-page-with-button.html",
+                           "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/");
+      doc.body.appendChild(iframe);
+      await new Promise(r => iframe.onload = r);
 
-    let portal = await createPortal(doc, new URL("resources/simple-portal-adopts-predecessor.html", location.href));
-    let iframe = doc.createElement("iframe");
-    iframe.src = new URL("resources/focus-page-with-button.html",
-                         "http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/");
-    doc.body.appendChild(iframe);
-    await new Promise(r => iframe.onload = r);
-
-    await portal.activate();
-    doc.body.removeChild(portal);
+      await portal.activate();
+      doc.body.removeChild(portal);
 
-    iframe.contentWindow.postMessage("focus", "*");
-    window.onmessage = t.step_func(() => {
-      assert_unreached("button inside x-origin iframe inside a portal should not be focused");
-    });
-    await new Promise(r => t.step_timeout(r, 500));
+      iframe.contentWindow.postMessage("focus", "*");
+      window.onmessage = t.step_func(() => {
+        assert_unreached("button inside x-origin iframe inside a portal should not be focused");
+      });
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      win.close();
+    }
   }, "test that a x-origin iframe inside an adopted portal cannot steal focus");
+
+  const TAB = "\ue004"; // https://w3c.github.io/webdriver/#keyboard-actions
+  promise_test(async t => {
+    let portal = await createPortal(document, "resources/focus-page-with-button.html");
+    try {
+      portal.tabIndex = 0;
+      await test_driver.send_keys(document.body, TAB);
+      portal.onmessage = t.step_func(e => {
+        assert_unreached("button inside portal should not be focused");
+      });
+      await new Promise(r => t.step_timeout(r, 500));
+    } finally {
+      document.body.removeChild(portal);
+    }
+  }, "test that we cannot tab into a portal's contents");
+
 </script>
 </body>
