Works great in FF4, 64bit Ubuntu 10.10.
Firefox 5 works just fine with it and I assume so does 4.1.
I´ve posted it before I believe, but here’s a pure CPU realtime pathtracer including source code from a year ago. It runs in the browser as well. It really is no rocket science.
You should check out his other apps, flakerenderer, landscape ray marcher, volumetrics, realtime hair…