Worth a try:
* Close Firefox.
* Click the shortcut for Firefox Safe Mode (located in the Start Menu).
* In the dialogue box that opens, tick the box that says 'Reset toolbars and controls'.
* Click the 'Make Changes and Restart' button.
This will undo any toolbar customisations you have made but providing the above has effected a cure, they can be re-done and all should then be OK.