I understand that, but why is it done that way? It's extra work to install it, and the fact that it's an extension probably means that it's not tested as well as normal browser UI. I really hate using extensions because I like to keep my software plain vanilla as possible to avoid strange bugs.
Because it's not the sort of feature that 90% of Firefox users would care much about. If you aren't aware of what it is and managed to accidentally activate it, you'd probably get really confused why you had to keep logging back into facebook.
