Had older version may have thrown away something important. Downloaded new Firefox when I try to open it, it says a copy of Firefox is already running and nothing happens.
Accidentally deleted some aspect of older Firefox, when I try to open new version it says there is a copy of firefox already open.
Did you delete the Firefox Profile Folder ?
If you did then you need to create a new profile. http://kb.mozillazine.org/Recovering_a_missing_profile http://kb.mozillazine.org/Profile_Manager
I have the same problem, I use Windows Vista