Firefox Covers Task Bar and Shut Down Bar Missing

There seems to be a problem running Compiz and Firefox together. At times, when expanding Firefox to fullscreen, it will expand beyond the taskbar, and the shut down/minimize bar will also appear too high up, effectively off the top of the screen, making it impossible to shut down Firefox by the usual method.

Whatever the problem is, once it's happened, it saves to the Firefox settings file, meaning the setting effectively sticks.

To remedy the problem either (a) turn off Compiz, or (b) type the following into a console:

mv ~/.mozilla ~/.mozillaold

This will rename your Firefox settings file. You will lose all of your extensions using this method, and any themes you may be using, so a re-install of them will be necessary.