Ok... it downloads 22MB of ogg and webm files and then does nothing for me. Just a black screen after clicking on continue. FF4 with GeForce 9600 GT on Windows XP 32-bit
If you type "about:config" in the location bar, and you search for a key called "webgl.disabled", is that true?
You may also have old drivers for your video card - though pretty much all the drivers in the past few years have OpenGL.