I find that launching the second (either by using the context menu or by dragging the tab) window causes Firefox to begin consuming memory as if it is processing something. I have watched it get to 300MB of RAM, steadily climbing without any interaction from me. By closing the new window (right click on the window's icon on the task bar and click "close") and giving it a minute or so to sort itself out, will save you having to end FF entirely, especially if you've got a number of tabs open already. This is one of the most useful aspects of the application, and I really miss it.

Thank you for the information. I sure hope they fix it. I miss this feature. :)