• In Firefox 3.6 versions on Windows and Firefox 4 on Windows and Linux it's possible to hide the "Menu Bar" via "View > Toolbars" or via the right-click context menu of a toolbar.
• Press F10 or press and hold the Alt key down to bring up the "Menu Bar" temporarily.
• Go to "View > Toolbars" or right-click the "Menu Bar" or press Alt+V T to select which toolbars to show or hide (click on an entry to toggle the state).

See also:

• Restore the Menu bar in Firefox
• http://kb.mozillazine.org/Toolbar_customization

Omg, Thank you so much you save lives :) I was so worried I had to delete my Mozilla Firefox Again thank you lots :)

You're welcome