i cant exit full screen i tried F11 and F12 nothing worked on my dell laptop!!! GRRR

No answer or explanation, but as a longshot try clicking Alt and using the mouse/cursor from the menubar that should appear.

Only other suggestions are general ones

• safe mode - but do not make changes infirst dialogue window you see, just click on continue
• basic troubleshooting
  • or the more comprehensive http://kb.mozillazine.org/Standard_diagnostic_%28Firefox%29

If the problem is similar to some others, it may be worth considering temporarily disabling the babylon toolbar.