Closed Bug 1768353 Opened 1 year ago Closed 6 months ago

prefers-color-scheme - Dark theme detection broken in Fx100


(Firefox :: Theme, enhancement)

Firefox 100





(Reporter: jscher2000, Unassigned)


User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:100.0) Gecko/20100101 Firefox/100.0

Steps to reproduce:

Enable built-in Dark theme, check pages, install and enable Dark Space theme (, check pages, use about:debugging to test a modification to Dark Space theme, check pages

Actual results:

With the default "Website appearance" setting of "Firefox theme" or "Nightly theme", the results are not as expected:

  • Built-in dark theme: about:home, about:addons, about:config, about:debugging, and about:preferences all have a dark background; Github ( has a dark background

  • Unmodified Dark Space theme: only about:home has a dark background

  • Dark Space theme with "color_scheme": "dark" added to the theme / properties key in manifest.json: same desirable results as built-in Dark theme

Expected results:

Firefox should continue to auto-detect which add-on themes are dark themes (i.e., add-on authors should not be required to explicitly add the color_scheme property).

For reasons I can't understand, Mozregression yielded:

2022-05-07T16:46:24.770000: DEBUG : Found commit message:
Bug 1736218 - Implement website appearance chooser. r=Gijs,fluent-reviewers,preferences-reviewers,flod

Differential Revision:

2022-05-07T16:46:24.770000: DEBUG : Did not find a branch, checking all integration branches
2022-05-07T16:46:24.771000: INFO : The bisection is done.

Perhaps that's not the correct commit??

Oh wait, this might be intentional:

Colorways and most AMO themes (unless they explicitly specify their color-scheme as per above) won't change prefers-color-scheme for websites anymore, and they'll follow the OS color-scheme by default. I'm personally not a fan of this decision, and think it's nice that when you choose a "dark" colorway like "Lush bold" content becomes dark by default, but UX folks disagreed with me and I don't mind that strongly as long as users can change it.


If so, can this be documented somewhere more obvious? The release notes don't mention it:

Users can now choose preferred color schemes for websites. Theme authors can now make better decisions about which color scheme Firefox uses for menus. Web content appearance can now be changed in Settings.


Component: Untriaged → Theme

The severity field is not set for this bug.
:dao, could you have a look please?

For more information, please visit auto_nag documentation.

Flags: needinfo?(dao+bmo)

Since this might be intentional, I'll set it as an enhancement to document the changes if it necessary in a better place.

Type: defect → enhancement
Ever confirmed: true

Yeah, this is working as intended.

Closed: 6 months ago
Flags: needinfo?(dao+bmo)
Resolution: --- → INVALID
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