Hi,
When portions of the context menu are disabled (to match custom menu button selections for particular user types), the menu has an odd appearance under Firefox. I actually only see this issue intermittently, but see it more often than not.
I couldn't test this on your demo because with the demo's radio buttons set to 'Minimal', the context menu is disabled. And with the demo editor set to 'Simple', the full menu is enabled.
Thanks,
Kazzlo