Above, you see the original Jumper and flixel framework code recompiled with Jangaroo AS3 to JS compiler, using a Jangaroo Flash API re-implementation, which implements Flash drawing using HTML5 canvas. This means it runs in every modern browser (for Microsoft Internet Explorer, you need version 9). For best performance, use Google Chrome or IE 9. Safari is also fast, but stops every other second (garbage collection?). Safari mobile (iPhone, iPad, iPod) works, but slowly, and the game does not support touch events. Firefox 3.6 is slower than Chrome, but steady, Firefox 4 beta 11 is faster. Opera 10 seems to work, too.
The button on the right-hand side loads the original Flash version of Jumper (and of course only works if you have a Flash-enabled browser).