I'm guessin you've already deleted your cookies and cache but if not that could be worth a try. You might also wanna take a look at you per site permissions to see if anything's amiss though I doubt that will be much help unless you find some glaring anomaly.

What OS are you runnin and what version of Firefox? You might try doin a search mentioning this issue relevant to the OS and version you're runnin and see if anyone else mentions similar issues and if so has a fix been found?

Just kinda pokin around here really, but hey, what could it hurt