I seeked into the API in order to write a plugin for myself. In order to aid my workflow I need to listen to two keystrokes closely followed.
Apparently there are only hacks available. I want to fire-and-forget about my plugin as long as the API to command firefox stays consistent.
I did not attempt to write any code (and any JS code, honestly that is) yet. Simply because I did not get that requirement addressed by the official API /& documentation.
Recompiling firefox would be the least favorable option; But I would still be hooked if it would enable me to observe keystrokes on my own.
As an practical example:
Pressing Shift two times in sequence and within 100 ms should enable me to eat the event.
To detect two keystrokes closely followed, you can use
EventListeners for theonkeyup/onkeydownevent. In combination with a variable that determines if the key was already pressed within the last 100 ms and asetTimeoutcall that resets that variable after 100 ms, it should be fairly easy to accomplish.