tor-browser

commit 64841b5dc9c79632d3321efe74fe2fc4631a0d16
parent af4baca06e2a8299a31a4a9fc74fa988d9ce0686
Author: Emilio Cobos Álvarez <emilio@crisal.io>
Date:   Mon, 15 Dec 2025 22:18:27 +0000

Bug 2006091 - Only use preferred-color-scheme override explicitly on our browsing context. r=jwatt

Otherwise let the embedder propagate the right information, which
matches how the page would render with the system setting without the
override.

Differential Revision: https://phabricator.services.mozilla.com/D276470

Diffstat:
M
layout/base/nsPresContext.cpp
 | 
7
++-----
M
layout/base/tests/test_emulate_color_scheme.html
 | 
39
++++++++++++++++++++++++++++++++++++---
M
modules/libpref/init/StaticPrefList.yaml
 | 
7
-------

3 files changed, 38 insertions(+), 15 deletions(-)
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
@@ -917,13 +917,10 @@ void nsPresContext::RecomputeBrowsingContextDependentData() {
   auto* top = browsingContext->Top();
   SetColorSchemeOverride([&] {
     auto overriden = top->PrefersColorSchemeOverride();
-    if (overriden != PrefersColorSchemeOverride::None) {
+    if (browsingContext == top &&
+        overriden != PrefersColorSchemeOverride::None) {
       return overriden;
     }
-    if (!StaticPrefs::
-            layout_css_iframe_embedder_prefers_color_scheme_content_enabled()) {
-      return top->GetEmbedderColorSchemes().mPreferred;
-    }
     return browsingContext->GetEmbedderColorSchemes().mPreferred;
   }());
 
diff --git a/layout/base/tests/test_emulate_color_scheme.html b/layout/base/tests/test_emulate_color_scheme.html
@@ -12,6 +12,8 @@
 }
 </style>
 <div id="test"></div>
+<iframe id="light-iframe" style="color-scheme: light"></iframe>
+<iframe id="dark-iframe" style="color-scheme: dark"></iframe>
 <script>
 function colorId() {
   // Gets the middle number of the rgb(0, x, 0) color.
@@ -21,20 +23,51 @@ function colorId() {
   return id;
 }
 
-{
+function iframeIsDark(id) {
+  return document.getElementById(id).contentWindow.matchMedia("(prefers-color-scheme: dark)").matches;
+}
+
+// Color-scheme switches should happen synchronously if we're the top window,
+// but if we're not (e.g., in the xorigin tests) we need IPC to go through
+// the embedder color-scheme mechanism, so we gotta wait.
+function maybeWaitForColorScheme(scheme) {
+  if (window.top == window) {
+    return;
+  }
+  let media = matchMedia(`(prefers-color-scheme: ${scheme})`);
+  if (media.matches) {
+    return;
+  }
+  return new Promise(r => {
+    media.addEventListener("change", r, { once: true });
+  });
+}
+
+add_task(async function() {
   let bc = SpecialPowers.wrap(window).browsingContext.top;
   ok('prefersColorSchemeOverride' in bc, "API should exist");
   is(bc.prefersColorSchemeOverride, "none", "Override shouldn't be active.");
+  ok(iframeIsDark("dark-iframe"), "Dark iframe is dark");
+  ok(!iframeIsDark("light-iframe"), "Light iframe is light");
 
   let originalColor = colorId();
 
   bc.prefersColorSchemeOverride = "light";
+  await maybeWaitForColorScheme("light");
   is(colorId(), 1, "Light emulation works");
 
+  ok(iframeIsDark("dark-iframe"), "Dark iframe still dark");
+  ok(!iframeIsDark("light-iframe"), "Light iframe still light");
+
   bc.prefersColorSchemeOverride = "dark";
-  is(colorId(), 2, "Dark emulation works");
+  await maybeWaitForColorScheme("dark");
+  is(colorId(), 2, "Dark emulation works as expected");
+
+  ok(iframeIsDark("dark-iframe"), "Dark iframe still dark");
+  ok(!iframeIsDark("light-iframe"), "Light iframe still light");
 
   bc.prefersColorSchemeOverride = "none";
+  await maybeWaitForColorScheme(originalColor == 1 ? "light" : "dark");
   is(colorId(), originalColor, "Clearing the override works");
-}
+});
 </script>
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
@@ -10003,13 +10003,6 @@
   value: false
   mirror: always
 
-# This pref controls whether the `prefers-color-scheme` value of iframes images
-# reacts to the embedder `color-scheme` in content.
-- name: layout.css.iframe-embedder-prefers-color-scheme.content.enabled
-  type: RelaxedAtomicBool
-  value: true
-  mirror: always
-
 # Controls the transparency of the initial about:blank document. Generally you
 # don't ever want a white flash in dark mode, but due to backwards compat we
 # have some extra control over this, for now at least.