Is it possible to hide title bar of Firefox 22 in OS X 10.8.4
Short answer: no

It has been a bug since firefox 13
Even though autohide is set to 'true' the toolbars won't hide in fullscreen.

Best option is to go to view -> Toolbars and uncheck the toolbars in the top menu
But this leaves the 'tab toolbar'

So if you really want to hide the toolbars you should open the page in a different browser.