Firefox doesn't apply websites' built-in dark themes even though Win11 is set to Dark Mode

Check that your website appearance is not set to light.
Settings and search for theme

If you have privacy.resistFingerprinting set to true, dark mode is permanently disabled.

Facebook doesnt seem to have a dark theme. There's no option for it as I see.
Might only be there if one logs in.

OP i 9001% feel you on the lack of dark mode support (and how 'inverting colors' has somehow become the best and most widely used "fix"*) but this isnt really a problem with firefox itself. i mean it is, but its not. its the fact that settings like this is where cooperation and standards meets capitalism and the ever increasing pressures of "do it, do it now, do it FAST" aka "move fast and break everything"

its complicated

see this post where a Mozilla Web Compat dev chimed in to explain the actual cause of a similar (albeit less impactful) bug. spoiler alert: standards say 'do thing', google doesnt do the thing, now theres a mismatch between the "rules" and the way things actually work so nobody knows whats going on and a lot of people are exploiting that for personal gain. weird how something as minor as favicon not displaying properly very simply and concisely sums up so many of the much bigger issues that effect a lot more than "just" the internet and tech. also metaphorically appropriate how the lack of support for dark mode would actually be solved if there was an actual standard for implementing two color layouts for websites, since most things exist in the grey area and most things are not an YES/NO or GOOD/BAD situation but at the end of the day the longer people ignore the problem(s) and the more people put on the spidersuit to point fingers at someone else eventually we're all trapped in spiderwebs or something idk it sounded really nice in my head but then the more i explained and wrote it just devolved into a stupid spiderman meme. ¯\_(ツ)_/¯ c'est la vie jajaja

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edit: its also a symptom of the very large and very obvious things that shouldnt be up for consideration on whether or not they are wrong or bad or immoral or whatever you wanna call it.

theres a quote ive heard about 'broken windows' and how that spirals out of control, quickly, and thought it was appropriate given the context of... well Mozilla v Microsoft (along with my other recent comments and the cause of those issues...)

so i was trying to find the one i was thinking of, and i guess you probably already know what the allegory of 'broken windows' is trying to communicate anyway - but i did find an interesting quote that actually explains the inverse:

People who leave their cars on the street with tape covering their broken windows are obviously too trusting. I mean, when your car did have glass for a window, someone broke into it. How is tape any more of a deterrent? What are the thieves going to say? Ooh, that like looks like duct tape, we can't beat that. Let's look for one with scotch or masking.

by "inverse" what i mean is while the person who said this probably isnt the one who broke the windows, hes criticizing the people who are already 'victimized' and thus making it worse. maybe not directly, but thoughts -> words -> actions and typically if someone has a shoddy vehicle or clothes or looks a little rough or whatever they probably are dealing with more real issues and actual stress in one day than this dude has ever dealt with in his entire life. usually i err on the side of "everyone has problems" but nah, the fact is, a lot of people have "problems" that others would call "blessings"

ill end it there otherwise ill be writing this all day but suffice to say f ck tr mp and anyone who doesnt understand why people say that deserves all the bad karma.

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final note: when people feel helpless against real, big, actual problems - whether thats an honest and true assessment or not - they are forced to put their blinders on, and thats how we get "tunnel vision" and "echo chambers" as well as why people get all worked up about things like a 16x16 pixel logo not appearing.