I'm used to middle-clicking tabs in Firefox, and finding myself instinctively middle-clicking taskbar icons, expecting it to close them, and annoyed when it opens a new instance instead. Is there something that can make this happen?
One of the very nice things that 7 Taskbar Tweaker can do is "Middle Click -> Close".
(Throw that man a bone! Here is a man who takes many of the idiocies that MS has thrown onto us & brings some common sense & thought to the table. MS should really pay him for his fixes.)