Removing Global Menu (Ubuntu 12.04)

To remove the global menu, either type...

 sudo apt-get autoremove appmenu-gtk appmenu-gtk3 appmenu-qt

... into a terminal, or remove "appmenu-gtk", "appmenu-gtk3" and "appmenu-qt" manually through the Software Centre.

N.B. To re-enable type into a terminal...

sudo apt-get install appmenu-gtk appmenu-gtk3 appmenu-qt

 Also disable the Global Menu Bar Integration  add-on in Firefox (Tools>Add-ons>Extensions.)