User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:87.0) Gecko/20100101 Firefox/87.0

Steps to reproduce:

Opened the bookmarks/history sidebar.

Actual results:

The sidebar still follows the Operating System's theme, not the current Firefox theme. This issue is most visible when using a dark Operating System theme with a light Firefox theme (or vice-versa).

Expected results:

The sidebar should be styled to follow Firefox's current theme. In older versions of Firefox, this wasn't a big deal, since much of the browser depended on the Operating System's theme. With the new Proton theme most of the browser is now manually styled, so it makes more sense to do so to the sidebar as well.

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Ah, I think we can fix this in the GTK code much better.

We're going to change the setup a bit to support both light and dark
system colors in the chrome process, like mac does. This is just
refactoring though.

Remove some unneeded IsContentProcess() check since it can't happen now
that we always enable RemoteLookAndFeel.

Err, that should've landed in bug 1707957, oh well.

https://hg.mozilla.org/mozilla-central/rev/03767acc6135

Backed out for causing valgrind failures.

Backout link: https://hg.mozilla.org/integration/autoland/rev/3b6178fd74b18ca31856c11a688caea992b1433c

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&revision=0fb0e3d056f8c73ac19a2c81f32e20935db0d19e&searchStr=valgrind&selectedTaskRun=LryxK1N5QLmdrY8o0Dd8pQ.0

Failure log: https://treeherder.mozilla.org/logviewer?job_id=337971274&repo=autoland&lineNumber=63906

Backout merged: https://hg.mozilla.org/mozilla-central/rev/3b6178fd74b1

Comment on attachment 9218708 [details]
Bug 1707872 - Extract per-theme data in nsLookAndFeel into its own struct. r=stransky

Revision D113542 was moved to bug 1708163. Setting attachment 9218708 [details] to obsolete.

No behavior change intended.

Also no behavior change intended.

Depends on D117226

This matches what macOS is doing in bug 1715145, and improves the
situation in the cases the user chooses a light Firefox theme, but a
dark GTK theme, or vice versa.

The nice thing of doing it globally is that we don't need to teach the
GTK code to paint with different color schemes in different windows,
which would be massively annoying.

This is expected to have an slight performance cost on startup for
light-theme users (as we need to read the dark gtk theme colors), but
it's hopefully ok.

Depends on D117227

https://hg.mozilla.org/mozilla-central/rev/35f93c68fc06
https://hg.mozilla.org/mozilla-central/rev/0e6c67113ca7
https://hg.mozilla.org/mozilla-central/rev/780b3e476e83