Rated 5 out of 5 stars

Hide Menubar is one awesome extension, and its author, yuoo2k, provides fast and excellent support if you ever have any problems.

And the latest version from his site now uses a Panel, so that in Thunderbird3 and Firefox4, the menu bar doesn't shove the window contents down, it just drops the menu bar down over the very top of the page (sadly the panel doesn't work in Firefox 3 in combination with TreeStyle Tabs and having tabs on the left because of a problem with Firefox)...

Anyway, 5 stars for both functionality and support... thanks yuoo2k!

This review is for a previous version of the add-on (4.0.20100901).  This user has other reviews of this add-on.