Movement/jump: cursor keys
Run/fire: A

Here it is...

Super Mario Bros. 1 (SNES) written in javascript. Have fun playing the game :-).

I know there are still some bugs and missing 'features' in the game, and you can't play the game smoothly in every browser. Internet Explorer sucks in fast movements, and with IE9 you can't play the game at all. The best browser to play Super Mario Bros. JS is the latest Google Chrome.
You can play the game up to world 2-1, and the sounds and music are disabled... for now.