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.