Answers:
Shouldn't be doing that lol. Could be a certain theme or extention you might have installed. I remember I had this theme called Pimpzilla, used to bounce so I unistalled. Try just opening Firefox's "safe" version. This opens a safe version that is very plain. Hopefully you should see the safe version listed.
I have firefox and never had this problem.It is an excellent browser.
I doubt it's a Firefox problem. Either your monitor is going bad or you need to update your video drivers.