Can't See the 3D Button in Firefox 11's DOM Viewer?

Yep, I had that problem too! First, go to: http://get.webgl.org/ If you get the error “…your browser seems to support webgl it is disabled or unavailable…”, here’s what fixed it for me:
  • about:config
  • search for webgl and make sure webgl.disabled is set to false and webgl.force-enabled is set to true
  • search for devtools.tilt.force-enable and set it to true
Hope that helps you too!