you know that thing that firefox on linux does, where if you click on the scrollbar it doesn’t just take you up or down a page like every scrollbar in the past thirty-odd years, but instead moves the scrollbar slider to where you clicked?
this is a gtk+3 thing, because GNOME’s UI team are relentless desktop innovators.
workaround: add this to ~/.config/gtk-3.0/settings.ini :
then restart firefox.
this being GNOME they will doubtless tch at people evading their superlative user interface vision and break it. until then, though, gtk+3 apps will work properly once more.