Are you sick of every single website using different fonts in the name of branding? You can easily force websites to use the browser default fonts:

  1. Preferences → Language and Appearance → Fonts and Colors → Advanced
  2. Un-check Allow pages to choose their own fonts, instead of your selections above

Alternatively (thanks to Ron for pointing this out) you can set browser.display.use_document_fonts to 0 to Never use document’s fonts. You can do this in about:config, or by setting it in your Firefox profile prefs.js, or, if you’re using NixOS, by setting it in programs.firefox.preferences.

Pros:

  • Most websites are easier to read.
  • Avoids downloading large font files. A decent page of text is single-digit kilobytes, but the fonts on a typical ~2021 website weighs in at over 100 kilobytes over 4 requests.

Cons:

  • Some websites have over-specified their layout, so things don’t align properly when laid out with another font. This probably means the site won’t work well in a lot of situations (niche browsers, ad blockers, without images, basically anything other than the browser the web developer is using), so it might be worth talking to the owners if you use the site often.
  • Some websites use icon fonts without fallbacks, so you might see one of those ugly .notdef glyphs instead of an icon.
  • It doesn’t always work.