Also using XP here. Make sure you're on the right bar (Firefox has way too many disparate developer tools). It's Ctrl+Shift+I to bring up the Inspector. There should be a button labeled "3D View" on the far right, next to "Style". I don't think it requires any sort of hardware acceleration, the computer I'm on right now isn't exactly recent...

If it's not there, you have to enable WebGL in the about:config.

Type about:config into the browser bar.

Right click and add a new boolean:

webgl.enabled_for_all_sites

Set to true, restart firefox, and load the site again. Press ctrl+shift+I, and you should see the 3D button in the lower right corner.

See this: http://support.mozilla.org/en-US/questions/923037

I believe it is determined by your video card. You could try fiddling with the about:config settings:

webgl.disabled webgl.force-enabled

Though it wouldn't surprise me if you started to get BSODs.