Rated 5 out of 5 stars

Please try to adjust for the expansion add Hide Titlebar Caption Plus (Smart) 2.1.6, thank you

This review is for a previous version of the add-on (1.8.71). 

One can do the same in my themes without 'Hide Caption' (Plus/Extra/etc)

In Firefox 4.0, put the tabs on top (which is default, and then hide menu bar (right click on the menu bar), and voila, with any specific Hide Caption extension (of which there are now multiple!) you can hide the caption bar yourself. All with the default Firefox support.