Rated 5 out of 5 stars

Great Addon!
Q1: I have installed HideMenubar 3.6, and restarted Firefox, but menubar is still there, it seems not working?
Ans: Right-click on menubar -> Uncheck the "Menu Bar".

This helped a lot! Might be better to hide the menu bar as default.

This review is for a previous version of the add-on (3.6.20100512).