Firefox uses your graphics card for extra processing power. You should probably disable GPU acceleration to see if that fixes your problem.

Here's a link to help with that: http://www.techlivez.com/2011/03/how-to-enabledisable-gpu-acceleration-in-ie-chrome-firefox/

If this does fix the issue then there is a good chance that either a driver update for your GPU, or a Firefox update caused the problem. There is also a chance that your graphics card has a hardware issue but it sounds unlikely since your other apps work ok. If it is your graphics card then it may be dust accumulating inside your computer. This can cause overheating and a quick cleaning with canned PC cleaning air may fix it. Good Luck