Tried it on different browsers, and wow, this is an alternative way to check the efficiency of the javascript-engines.

Opera and Chrome comes best out so far, with a steady 57-59 FPS. Safari says it comes with 30-33 FPS, but stopped rendering. It still emulated the game fairly well though. I heard I died from a mushroom @ the super mario bros emulator. Firefox had a measly 4-5 FPS.

I tried it with Internet Explorer as well, but it wouldn't start without the sound-engine made in flash. Obviously installing flash for IE isn't that easy, so I didn't bother.