Resolutions were made for csswg-drafts/#3857.

[mediaqueries-5] UA guidance on light vs no-preference

• RESOLVED: Remove the no-preference value
• RESOLVED: Add a note that no-preference used to exist but was removed due to lack of impl

Discussion.

It was removed from the spec. Bug 1643934 updates the WPT tests.

Though probably not blocked by this bug, https://bugzilla.mozilla.org/show_bug.cgi?id=1642366 removes the no-preference value from devtools as well.

Backed out for perma failures.

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&selectedTaskRun=QezyVLvpS8ib7oMw_ZrSsg-0&resultStatus=testfailed%2Cbusted%2Cexception&revision=bca9f7459a161e1bb7b9b4482694513ff76fde62

Logs:
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305638657&repo=autoland&lineNumber=6101
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305644716&repo=autoland&lineNumber=4675
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305638095&repo=autoland&lineNumber=6079

Backout: https://hg.mozilla.org/integration/autoland/rev/089af72b96ed33cccd1e6d761ce932de1d3ddc76

So as to not use a pref with an invalid value, which I would've changed
the behavior of with the previous patch.

I'll land the second patch. The first one still needs bug 1643934 to land. I saw an wpt-sync fly by and I didn't realize that wasn't part of it.

https://hg.mozilla.org/mozilla-central/rev/245776c0b467

Emilio: prefers-color-scheme is broken in Fenix (https://github.com/mozilla-mobile/fenix/issues/11556).

Working: AC 45.0.20200610130052 with GV 79.0a1-20200609092134
Not working: AC 45.0.20200612130101 with GV 79.0a1-20200611093454

And your patch landed between these two versions. Could it be that your patch caused the problem?

It seems possible, can you point me to how is A-C using GeckoRuntimeSettings?

I found https://github.com/mozilla-mobile/android-components/blob/master/components/browser/engine-gecko-nightly/src/main/java/mozilla/components/browser/engine/gecko/mediaquery/PreferredColorScheme.kt

But I don't really know the implementation. So maybe better ask one of the developers. 😅

https://hg.mozilla.org/mozilla-central/rev/52126fd9ffdf

(In reply to Sören Hentzschel from comment #12)

But I don't really know the implementation. So maybe better ask one of the developers. 😅

I took a look this morning, bug 1645770 fixes it.

Posted a site compatibility note for the change.

I've documented this removal; see https://github.com/mdn/sprints/issues/3424#issuecomment-652649191 for the full details.