Breaks Firefox pretty good. Turns all web pages blank with the added bonus of blanking out all the XUL stuff too. So dialog boxes pop up with nothing on them, including buttons, so you cant say OK or Cancel. Notice me not being able to close the preferences window in the after shot down there.

I doubt you'd ever want to install it, but there's no accounting for taste. You probably want to know how to get into safe mode to fix stuff if you do.