Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
Do NOT click the Reset button on the Safe mode start window or otherwise make changes.
By the way, if you use a Samsung system (esp. Windows 8 systems) and find that clearing the cache fixes it for a while but eventually problems recur, this could be due to a feature of the Samsung Help Center software. This is discussed in other threads.