Firefox has about:config prefs to block web content from using fonts other than their OS's default system fonts.
The pref names and their possible values:
# Visibility level of font families available to CSS font-matching:
# 1 - only base system fonts
# 2 - also fonts from optional language packs
# 3 - also user-installed fonts
layout.css.font-visibility.standard
layout.css.font-visibility.trackingprotection
layout.css.font-visibility.resistFingerprinting
Thank you for the link. I actually was wondering if there is a list of about:config properties and it seems that most of them are described in that YAML file.
The pref names and their possible values:
https://searchfox.org/mozilla-central/rev/de15f9c109f9c474d0...Here's the Firefox bug about enabling these prefs, probably in Tracking Protection Strict mode to start: https://bugzilla.mozilla.org/show_bug.cgi?id=1736005