User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:96.0) Gecko/20100101 Firefox/96.0

Steps to reproduce:

1. Update to the latest nightly build.
2. Restart and launch Firefox.

Actual results:

1. Tab bar becomes white even if it is using dark theme.
2. This happens on both Windows and Mac builds.

Expected results:

Tab bar should be in dark gray/black according to the chosen theme

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

I am encountering the same issue on Linux. I am unable to reproduce it with a fresh profile. However, I am able to reproduce it by creating a profile that uses the Dark theme on an older build, then opening that profile with a newer build:

1. mozregression --profile mytestprofile --profile-persistence reuse --launch 2021-11-18
2. Enable "Dark" theme in Addons and Themes (Ctrl+Shift+A).
3. Close Firefox.
4. mozregression --profile mytestprofile --launch 2021-11-20

Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=0bcb58dfabccf48b9acf7807249e381bd64f2dc2&tochange=8c47ea74111483c4594aa139a11e60d7ef6dde6d

Which suggests it was regressed by Bug 1742111. Note that Bug 1741900 has a similar title, but I'm observing this issue on all windows, including ones created long after initialization, so I don't believe it is the same issue.

I saw this bug today as well once. Then I switched to another theme (firefox-compact-dark) and back (abstract-bold-colorway) and the bug was apparently gone. It did not come back after a restart.

(In reply to Darkspirit from comment #4)

I saw this bug today as well once. Then I switched to another theme (firefox-compact-dark) and back (abstract-bold-colorway) and the bug was apparently gone. It did not come back after a restart.

I saw this too with Colorways Cheers Bold.
Since Colorways themes will be removed in the future if they are not enabled (I don't know how it exactly works; maybe I misunderstood it), does this workaround (disable Colorways > immediately re-enable) really works for Colorways themes?
Let's hope Firefox users do not lose their temporary theme when another similar bug happens.

(In reply to Darkspirit from comment #4)

I saw this bug today as well once. Then I switched to another theme (firefox-compact-dark) and back (abstract-bold-colorway) and the bug was apparently gone. It did not come back after a restart.

Same here. Changed to light theme and then dark theme again and the bug was gone.

(In reply to Darkspirit from comment #4)

I saw this bug today as well once. Then I switched to another theme (firefox-compact-dark) and back (abstract-bold-colorway) and the bug was apparently gone. It did not come back after a restart.

I had this issue too, with a custom third-party theme applied. Disabling/enabling it fixed the coloring for me.

Same here with a darkish AMO theme except it turned the text on tabs and menubar/bookmarks toolbar black and the 'about:' pages light until disable/enable of theme. As in comment 3, only occurs on initial update.

Happened after update to 20211121101729 again (once).

Nightly 96.0a1 20211121101729 has bug 1742111 backed out.

Testing verifies going from an old unaffected build to the latest Nightly doesn't experience the issue as does updating from old unaffected to affected to latest Nightly if the user doesn't modify themes while the affected build is being used.

So yesterday I had the theme, I went to light and again dark and it was fixed
Today: I'm not sure if an update was pushed in the last hour, an hours ago it was fine but just now I had the same bug again with 20211121101729 and I fixed it again by changing the theme to light and dark again.