I am using Firefox as usual.
Multiplayer guest-mode: standard situation is that you connect with a player nickname "guestXXX", where XXX is you temporary ID. All stats are saved only as a session, so when you restart the game/browser, the progress of stats is lost forever. You can copy functionality from castle wars (http://www.kongregate.com/games/m0rkeulv/castle-wars-2). I am not sure what is in your multiplayer, but maybe it will help with my idea of guest? :)