if Vimium's DOM node is focused, then stop key events
if Vimium's DOM node is focused, then stop key events

This fixes a bug that a keyCode 229 is given by a Chinese IME for each
keydown event, while for keyup event, keyCode changes to the real one,
which made Vomnibar fail holding all of its text inputing events.

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus