I have the same problem. Same OS too.

Similar problem for me : I get a black screen on startup. Then some times when I open new tab, or each time I customize the interface : the black screen appears for a couple of seconds. Another issue: occasionally the firefox window sparkles, it's very disturbing.

(Windows 7 64bit)

Turn off "hardware acceleration" in tools/options. Worked for me.

I had a simular problem where menus and the url suggestions box flashes whenever I move the mouse or types a character. Turning off hardware acceleration worked for me.

Thanks. It seems to have worked, so far at least!

Actually, I have to rectify the previous post. Even after turning off Harware Acceleration I still have the same problem, or maybe somewhat less frequently.

At the risk of sounding like an idiot, where has Tools/Options gone?

I can't find any tools menu in the new Firefox, and searches for options for turning off hardware acceleration are turning up nothing.

I have the same issue...downgraded to 3.6

Same here. And since some of the tools I use (Google Toolbar, McAfee Siteadvisor) aren't ready for version 5, I won't be installing it until they are.

This problem appears to have been fixed in Firefox 5, even with hardware acceleration turned on