I wish I knew. I detest Firefox 4, and it gets worse every time I see that idiotic, anthropomorphic bear/panda or whatever it's supposed to be. The installation disabled my HP web smart printer pack. Someone should tell these guys that change for the sake of change is regression. 3.16.16 was as near perfect as it could be for me, and it seems to be impossible to reinstate it once it's been replaced by 4