This worked for me on Windows 7 Dell Laptop running FF 5
by eylai - 8/11/11 11:19 AM
In Reply to: Using Firefox my right click menu disappears in a flash. by nasacouk
This solution worked for me (Dell E6320 laptop running Firefox 5 on Windows 7 Pro) immediately:
Go to Options > Advanced > General and uncheck the "Use hardware acceleration when available"
I found it here: https://support.mozilla.com/en-US/questions/764278#question-reply
It's a pity that you might be slowing the rendering somewhat, but the tradeoff is well-worth it...