If you drop the control in an ASP.NET page and do a refresh page in FireFox, the status bar keeps showing "Transfering data from local host..." even though the page should have loaded and is done. When you tab away to another tab and back, the status bar clears up. This only happens in Silverlight mode, not Flash. I don't know if this is a FireFox issue, Silverlight plugin or the the upload control.
Any ideas?