My firefox works perfectly. Never had any issue. Only 2 addons I am using are adblockplus and flashgot.
Check your ff version. Most recent version is 16.2. Also, check your flashplayer and java engine's version. Update if necessary.
If all that doesnt help, try clean your cache of all cookies and offline data.
If it still wont work, use firefox's safe mode---it boots firefox with no addons or extentions at all.
Last thing is using another browser. If the problem persists, it could be your hardware problem.
EDIT: I saw you are using some themes for your FF. Try disable them and see if it works. Sometimes 3rd party themes are the ones to blame.
Bitten By Mod Bug Again