This appears in MT3.0D and 3.01D, using FireFox 0.9.2 (and previous versions of FireFox).

Right-clicking in the MT interface, for such normal purposes as copying and pasting text into an entry or a template produces a pop-up reading:



The copy/paste operation works once the popup has been cleared.

It's an irritation rather than a major problem, but I'd be happier if it went away.....

Are you using the Tab Browser Extenstion in Firefox? I found that uninstalling that made the error go away. And now that I'm back to using an official release(0.8) of FireFox with TBE, I'm not getting the error anymore.

Hope one of those ideas helps.
Kristine