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: #

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 https://searchfox.org/mozilla-central/rev/de15f9c109f9c474d00faf8032f559c236067c06/modules/libpref/init/StaticPrefList.yaml#7622-7641 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 https://bugzilla.mozilla.org/show_bug.cgi?id=1736005