This. Plus worth mentioning that Firefox has native support for real user stylesheets with own origin layer, just as specified by standards. It is userConent.c

This. Plus worth mentioning that Firefox has native support for real user stylesheets with own origin layer, just as specified by standards. It is userConent.css file in the "chrome" folder in the profile directory. Slightly cumbersome compared to Stylus' provided "UserCSS" injections, but I think it is super important for any user agent to keep this functionality that is by the way required for CSS2.1+ compliance, and UAAG [1] And also, to my knowledge, Firefox is one of few browsers that lets you (still) hack its interface ("chrome") through css (userChrome.css in aforementioned folder). [2] [1] https://www.w3.org/TR/2015/NOTE-UAAG20-Reference-20151215/#sc_173 https://www.w3.org/TR/2015/NOTE-UAAG20-Reference-20151215/#s... [2] https://twitter.com/myfonj/status/1387584962354982912 https://twitter.com/myfonj/status/1387584962354982912