In browse mode in Mozilla applications, pressing enter on a button, etc. no longer fails to activate it (or activates the wrong control) in certain cases such as the buttons at the top of Facebook.
_activateNVDAObject in the Gecko vbuf now tries doAction on ancestors before it tries clicking. It tries doAction even if the button is off-screen/invisible. Also, it does not try to click objects with the invisible state or a width/height of 0.
Fixes #4106.