For an example I'll take the recent Discord offence of hooking [ctrl]+[shift]+[u] to file uploading even though it's a universal combo for entering unicode characters like √ (U+221A) by value. I'd like to be able to tell firefox to never allow any website, app, whatever inside it's environment to hook that key combo. This could be implemented by just not providing the event for that key combo when it's detected, thus preventing the website etc from ever receiving the key combo in the 1st place, let alone reacting to it.