YOU YOU ARE NOT USING A BROWSER THAT SUPPORTS THE HTML5 <canvas> FEATURE.

Original code found in this blog post. Here's a direct link to the HTML5 test page..

Changes I've made to original code: (a) eliminated two spurious redraws of entire background; (b) removed some CSS so you can see the framerate more easily when zooming, etc.; (c) removed empty div tag to make valid html5 (allowing these comments to remain visible); (d) changed background color of page to show transparency in canvas; (e) filled the background (once) at the beginning; (f) reduced the part of the ground that gets redrawn to just the bit under the ball (and even that is excessive); (h) removed the 60fps framerate cap; (i) replaced the stupidly complex and inefficient fps code with a running weighted average.