update UA stylesheets

resources/in-content/root.css

@@ -56,12 +56,6 @@
     font-weight: 300;
   }
 
-  @media not print {
-    img.transparent {
-      background: var(--transparent-img-background) !important;
-    }
-  }
-
   @media (prefers-color-scheme: dark) {
     :root {
       color: var(--plaintext-color) !important;

resources/layout/contentaccessible/ImageDocument.css

@@ -26,6 +26,11 @@ body {
   }
 }
 
+.isInObjectOrEmbed {
+  width: 100%;
+  height: 100vh;
+}
+
 img {
   display: block;
 }

resources/layout/contentaccessible/TopLevelImageDocument.css

@@ -8,15 +8,18 @@
   are top level (e.g. not iframes).
 */
 
+@import url(chrome://userchrome/content/layout/uc-low-globals.css);
+
 @media not print {
   img {
     text-align: center;
     position: absolute;
+    inset: 0;
     margin: auto;
-    top: 0;
-    right: 0;
-    bottom: 0;
-    left: 0;
+  }
+
+  img.transparent {
+    background: var(--transparent-img-background);
   }
 
   img.overflowingVertical {

resources/layout/contentaccessible/TopLevelVideoDocument.css

@@ -8,20 +8,18 @@
   are top level (e.g. not iframes).
 */
 
-body {
+:root {
+  background-color: black;
+  /* Fill the viewport height, so that our '-moz-user-focus' styling will
+     disregard clicks in the whole background area (so the video element
+     doesn't inadvertently lose focus from a stray click on the background). */
   height: 100%;
-  width: 100%;
-  margin: 0;
-  padding: 0;
   -moz-user-focus: ignore;
 }
 
 video {
   position: absolute;
-  top: 0;
-  right: 0;
-  bottom: 0;
-  left: 0;
+  inset: 0;
   margin: auto;
   max-width: 100%;
   max-height: 100%;
@@ -30,5 +28,5 @@ video {
 }
 
 video:focus {
-  outline-width: 0;
+  outline-style: none;
 }

resources/layout/contentaccessible/details.css

@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+slot:not([name]) {
+  display: none;
+}
+/* Either the fallback summary (inside the shadow tree), or the slotted main
+   summary. */
+summary,
+slot[name=internal-main-summary]::slotted(summary) {
+  display: list-item;
+  counter-increment: list-item 0;
+  list-style: disclosure-closed inside;
+}
+:host([open]) summary,
+:host([open]) slot[name=internal-main-summary]::slotted(summary) {
+  list-style-type: disclosure-open;
+}
+:host([open]) slot:not([name]) {
+  display: revert;
+}

resources/layout/contentaccessible/plaintext.css

@@ -16,7 +16,9 @@ pre {
   white-space: pre;
 }
 
+/* Make text go with the rules of dir=auto, but allow it to be overriden if 'Switch Text Direction' is triggered */
 html:not([dir]) pre {
+  /* Not a UA sheet, so doesn't use :-moz-has-dir-attr */
   unicode-bidi: plaintext;
 }
 
@@ -33,6 +35,12 @@ html:not([dir]) pre {
   }
 }
 
+/* NOTE(emilio): For some reason some pages, mainly bing.com, load a bunch of
+ * scripts in zero-size <object> elements, see bug 1548449.
+ *
+ * Line-breaking such documents is useless and pretty expensive, so only render
+ * them if there's a viewport. Sigh.
+ */
 @media (width: 0) or (height: 0) {
   :root {
     display: none;

resources/layout/uc-low-globals.css

@@ -19,4 +19,8 @@ tooltip {
   --tooltip-border-radius: 3px;
   --tooltip-border-color: var(--uc-menu-border-color);
   --tooltip-box-shadow: 0 0 5px hsla(0, 0%, 0%, 0.2);
+  --transparent-img-background: center/16px repeat hsla(0, 0%, 80%)
+    url(chrome://userchrome/content/checker.svg);
+  --transparent-img-background-context: center/16px repeat
+    url(chrome://userchrome/content/checker-context.svg);
 }

uc-globals.css

@@ -139,11 +139,6 @@ but other than that these variables should be available everywhere. */
   --global-focus-shadow: 0 0 0 2px var(--global-focus-shadow-color);
   --global-focus-outline-offset: -2px;
 
-  --transparent-img-background: center/16px repeat hsla(0, 0%, 80%)
-    url(chrome://userchrome/content/checker.svg);
-  --transparent-img-background-context: center/16px repeat
-    url(chrome://userchrome/content/checker-context.svg);
-
   --acrylic-blur: blur(15px);
   --acrylic-texture: url(chrome://userchrome/content/texture/lightnoise.png);
   --acrylic-blue: hsla(233.3, 39.1%, 9%, 0.58);