I'm having that problem in Firefox too. The more pressing problem that's started because of the recent update, though, is that it frequently starts with only some or none of the extensions available. The add-ons window says that they're enabled, but they're not, and restarting Firefox doesn't help.

Oh yes, and sometimes the search bar (for Google and Wikipedia and stuff) just stops working. I think this is the most problems I've ever had with a Firefox update.