No extension—even Netscape 1.0 had most of this stuff built in. I use Pale Moon as a primary browser, but the settings required still exist in modern Firefox, under General > Language and Appearance > Contrast Control and General > Language and Appearance > Fonts > Advanced. Note that although the font labels may say “Serif” etc., Pale Moon at least doesn’t care what you put there—you can set “Serif” to a sans font if you like, or vice-versa.
Of the Chrome-based browsers I have lying around for work and emergency purposes, Vivaldi has the font settings under Webpage, but doesn’t have full webpage colour settings (although you can force a dark theme, which might be enough). Chromium has the font settings under Appearance > Customize Fonts, but lacks anything that looks like useful colour settings.
If you’re looking for browser extensions that will restore the colour-forcing functionality for Chrome-based browsers, “Accessibility” is one category to look under.


Not unless they’re complete boneheads (which, admittedly, is not impossible). If they do that, they effectively lose embed-video-in-external-sites functionality, and that might just be enough for unpaid content creators to dump the platform en masse and cause their effective monopoly to crumble. The content creators who are actually making decent money may never leave entirely, but if another viable platform comes into existence, I bet most of them would mirror to it.