I've been using Firefox exclusively for about a year now, and I obviously utilize tabs quite a bit.  I've gotten used to having all my "browser windows" open in the same window.  That's why I get really mad when stupid sites automatically open a new window when I click on a link.  I think the choice should be left up to the end user, not the web designer.  On a whim, I remembered that Firefox has a few options for tabs (Tools -> Options -> Tabs).  I enabled the option "Force links that open new windows to open in -> a new tab".  Initially, this check box wasn't checked at all.  After I checked it, I had it set to "the same tab/window as the link", but this caused some problems like navigating away from Gmail and Bloglines (which are two tabs I keep constantly open).  After changing it to "a new tab", I get no more new Firefox windows.  Problem solved. #technology