recently I stumbled upon this experiment extension https://github.com/jingyu9575/privileged-mouse-gestures
it works really well already, while it may need some extra polish the general API looks pretty solid, I don't know if the author contacted you regarding this, but what would you think about implementing the API in the browser? it's one of the most missed things after the sunsetting of classic extensions and this is much better option than injecting the loader and manually managing scripts
