http://support.mozilla.com/en-US/forum/1/615659
Can’t see the Menu Bar (File, Edit, View, History…Help)? Hold down the {ALT} key ({Cmd} key in OSX) and press the following letters in this exact order: V T M
The Menu Bar should now be displayed permanently, unless you turn it off again (View > Toolbars). Turning the Menu Bar on and off is a new feature in version 3.6.
I’m having the same problem