Opera isn't OSS. In the modern world, Opera and Mozilla have been in a neck-and-neck feature race for years while IE has stagnated. But I hear that IE may get popup blocking and tabbing with XP SP2 (leaving W2K IE users with no MS browser upgrade). Who's copying?
And one thing that will fry the minds of Microserfs everywhere: The latest Mozilla/Firefox is actually smaller and faster than its predecessor even with the new features.