1749377 - Windows opened from dark PBM windows should inherit dark theme

Status: RESOLVED FIXED

(Firefox :: Theme, enhancement)

Description

[Paul Zühlcke [:pbz]]

For privacy segmentation we apply dark themes to private browsing mode windows.
Windows which have a contextual relationship to the private browsing windows should inherit their dark theme. This includes:

• page info window
• prompts (via nsIPromptService)

Windows which are launched from the PBM window, but are generally global, such as the library (history, bookmarks, etc), should not inherit the style.

Comment 1

[Paul Zühlcke [:pbz]]

I've done some experiments with the BrowsingContext flag prefersColorSchemeOverride. While not originally implemented for the purpose of this bug, it can be used to override the color scheme per browsing context and therefore per window.

In pageInfo.js I can check whether the parent window is in PBM and apply a dark color scheme.
This works well on Windows. On Linux it only works partially: a small portion of widgets remain dark, resulting in low contrast. On macOS it doesn't work properly: The window background remains light, only the text color is updated, which makes the text very hard to read.

We could use a similar approach for prompts, the commonDialog.xhtml document. Again, it doesn't work properly on macOS. Also, I found that setting prefersColorSchemeOverride for embedded prompts/browsers leads to a crash:

Hit MOZ_CRASH(CanSet failed for field(s): PrefersColorSchemeOverride) at /home/pbz/moz/build/debug/dist/include/mozilla/dom/SyncedContextInlines.h:102

Which means the approach currently only works for window prompts.

Comment 2

[Paul Zühlcke [:pbz]]

Attachment: Bug 1749377 - Use prefersColorSchemeOverride to inherit dark PBM theme for prompts and pageInfo window. r=#desktop-theme-reviewers!,Gijs!

Comment 3

[Paul Zühlcke [:pbz]]

Attachment: Bug 1749377 - Move browser.theme.dark-private-windows to static prefs. r=emilio!

Depends on D136931

Comment 4

[Paul Zühlcke [:pbz]]

Attachment: Bug 1749377 - Set color scheme on window widget to fix PBM dark theme issues on macOS. r=emilio!

Depends on D136932

Comment 5

[Paul Zühlcke [:pbz]]

Attachment: Bug 1749377 - Tests for dark pageInfo and prompts. r=dao!

Depends on D136933

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/83581637ae08
Use prefersColorSchemeOverride to inherit dark PBM theme for prompts and pageInfo window. r=desktop-theme-reviewers,dao
https://hg.mozilla.org/integration/autoland/rev/46cbaff8614d
Set color scheme on window widget to fix PBM dark theme issues on macOS. r=emilio
https://hg.mozilla.org/integration/autoland/rev/e3e0c8d40916
Tests for dark pageInfo and prompts. r=dao

Comment 7

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/83581637ae08
https://hg.mozilla.org/mozilla-central/rev/46cbaff8614d
https://hg.mozilla.org/mozilla-central/rev/e3e0c8d40916