FF4 has a feature by which, when you try to open a second copy of a page, will flip to the existing tab rather than re-opening it.
This drives me crazy.
I usually have several dozen tabs open, across multiple screens, some not visible. When I re-open a tab I want it to appear right in front of me. Not (as happens now) to be brought to the front of a window I can’t even see.
this blogpost offers some solutions, most of which don’t seem to work.
What does seem to work is adding some junk to the end of the url. A hash should do it, or in extreme cases a hash followed by some random characters.