Earlier quoted context omitted.
Mozilla is developing an add-on called Go Faster that uses WebCompat data to adjust settings in Firefox for compatibility on poorly tested sites. https://github.com/mozilla/webcompat-addon https://wiki.mozilla.org/Compatibility/Go_Faster_Addon/Overr... https://webcompat.com/
Firefox already ships some UA overrides. You can see the list of active overrides (with links to bug reports explaining each) in Firefox's about:compat page.
https://hacks.mozilla.org/2019/07/firefox-68-bigints-contras...
Good to see this in action already.