Thanks Rated 5 out of 5 stars

Works for me. This addon seems to be the only way to make Firefox under Linux hide the titlebar (not using KDE). This is why I give it five stars even though it has a little flaw: if you open enough tabs, the last one gets overlapped with the minimize, maximize and close buttons.

This review is for a previous version of the add-on (1.6.1-signed).