As many of you have pointed out to me, the v2 control does not support firefox as well as the Windows Live Local site does. There is actually a wedge you can put in place to fix most of these issues, but it is not officially part of the SDK today.
To use the wedge, add the following line to your html as the first line in the body element:
<![if !IE]><script src="http://local.live.com/JS/AtlasCompat.js"></script><![endif]>
After this is added, your application should start showing properly in FireFox. Try it out, let me know if it works for you.
Moving forward, we will build this support into the control.
THE DISCLAIMER: As I said above, it is not officially part of the SDK and is unsupported (but still send me bugs you find! as we will try to fix them). When we release our next version we may break your application by updating, moving, removing this file.