Here is the problem: I'm trying to refspoof wall street jr. website (wsj.com) with digg.com since wsj.com submits its restricted content to digg.com. When I try to do that I get this error message from firefox

"the refbar is used as input and it only works with just one open browser window -- use tabbed browsing"

I'm pretty sure that I have only ONE firefox window open... what's going on here? It seems that I have some invisible firefox window open...