Why does Firefox 4 tap out?

Every time I start Firefox, the dark blue bar at the top turns pale, and I can't click anywhere in the browser. All of my other programs still work fine, like Microsoft Word, so I know it's just Firefox freezing up. Interestingly, I found that hitting Alt+F4 actually unfreezes Firefox, so I'm guessing there's some hidden dialog box that I'm closing. I have no idea why this is happening. Possible relevant information is that I use NoScript, Ghostery, and FastestFox add-ons. Halp?