Firefox 3 introduces real full screen mode where unlike Firefox 2 where the location bar and tab bar remained visible at all times, now they both automatically hide below the top edge of the screen.
If for some reason you prefer to see the location and tab bars, you can customize Firefox:
- Enter about:config in the location bar to access the advanced preferences.
- Look for browser.fullscreen.autohide and double click it to set it to false.
Or you can just turn off the toolbars slide up animation:
- Look for browser.fullscreen.animateUp, right-click, select Modify and enter 0.
As with all advanced preferences you can reset them to their default values right-clicking and selecting Reset from the context menu.
Just in case, you enter full screen mode pressing F11 or selecting Full Screen in Firefox’s View menu.