It would improve both discoverability and usability.
1. Discoverability: These features, despite being older than every web browser available today, seem relatively unknown. Unfortunate because it alleviates two problems I think are probably common:
▶ First: I grew up with myspace and like things to look how I want
▶ Second: accessibility
▶ The secret third one: a mix of one and two with built in dark mode that is superior to chromiums invert colors version and any third party extension dark mode.
2. Usability: Since I started complaining about this problem, then discovering Firefox already solved it, then posting how awesome a feature it is, it does seem like (from my terminally online first hand experience) more websites have started preferring the slightly different settings Firefox uses instead of other browsers - but still some that are in between or have a dark mode/high quality accessibility settings built in, or just generally don't work well with the Firefox override (like when filling in forms, configuring display settings for other websites (like this post, for example), etc). Thus, while not super common, I do find myself needing to turn the override off and on somewhat often, and it is tedious to switch tabs and would be much easier if the settings were in the sidebar.
I have tried to poke around in the code to see if it was something a non-coder could figure out with the help of an AI but soon learned it was not gonna happen that way lol - but despite that it does seem like something that would be a quick thing for someone who does know what they are doing. Maybe.
