It looks like Firefox can't find some files for the integration of Webapps into Unity. On my machine (Ubuntu 12.10 64 Bit as well), those scripts are located at
/usr/share/unity-webapps/userscripts, your installation is looking for them at
/usr/local/share/unity-webapps/userscripts. In other places I also read about paths like
/usr/share/gnome/unity-webapps/userscripts. My assumption is that in the course of development those path has been changed, and your installation is not using the same version of the path in all places.
The package responsible for the integration is
xul-ext-websites-integration. Maybe this package, for one reason or another, is not at the correct version in relation to your Firefox package and needs to be updated? The version on my machine is 2.3.5-0ubuntu1. It might help if you reinstall that package.
Another chance might be to uninstall that package. But it is a dependenceny of
xul-ext-unity, so you would need to uninstall that, too, and you would probably loose all of Firefox' integration into Unity. So I would do that only as a last resort.