Sorry... `input` is a bad idea because it will not have keycode and won't return any event while press back in empty input case, which could not satisfy the requirement in #15118.
Except for the trigger timing difference, keyup/keypress will return different keycode from gecko. keypress only has charcode and return 0 for keycode, but keyup/keydown only has keycode and return 0 for charcode. Hi @rwaldron, is this result matches what you see in #15118? I only tested it on browser and it seems we should apply keyup for this case.