can someone tell me how to get this to actually work? I'm on firefox 15 and I don't see this feature?
You have to open the inspector first (Ctrl+Shift+I or Firefox->Web Developer->Inspector), and then click the "3D" button on the bottom left (or bottom right if you're on some beta/nightlies).
Unfortunately it requires webgl which I don't have on any pc. I couldn't find any easy way to install it.