Currently to make it work you have to run it locally after downloading from github: https://github.com/maroslaw/rainyday.js In Firefox it runs fine at the beginning but then the fps decreases (running in 1920x1200), in Chrome it's "better" because it seems to use both CPU cores fully on a dual core while Firefox uses only one. Anyways it should use the GPU more (using WebGL) and not so much the CPUs, but i understand it's one of the developer's "first contact with JavaScript" and using shaders would be a little harder for him but here are some introductions: http://www.html5rocks.com/en/tutorials/webgl/shaders/ http://aerotwist.com/tutorials/an-introduction-to-shaders-pa...