The Unity plug-in has produced some impressive browser games, but maybe Lego Star Wars the Quest for R2D2 is the best so far.  It's basically a 3D hack and slash adventure, but has great graphics, is really smooth and of course has everyone's favorite Star Wars sound effects. Pressing F puts you in full screen mode, and then you won't even notice it's a browser based game. Not so long ago, a game like this would have been perfectly acceptable on a home console, and it's incredible to see this for free running in Firefox! Play Lego Star Wars the Quest for R2D2 here. The Unity plug-in is available for Windows and Mac.