Replaces the standard menu bar with a tiny menu popup, which you can then move to the Navigation toolbar.
This is good for those of us using the Gnome desktop under Linux; since it saves you some vaulable screen real estate and helps stop your browser window feeling letter-boxy at 1024x768.
(Also, yes, I have been away from updating for a couple of weeks - just moved house and have finally got a new 'net connection).