One nitpick I have with the tab system of Firefox is that to close a tab with a mouse I have to click on a tiny x in the upper right corner. Although I usually just use the Command-W combination, certain times call for a mouse click. If you don’t hit the X just right you will click a blank space which produces another tab.

Tab X takes care of this by adding Xs to all the tabs so now I can clear individual tabs without having to right-click on it. Why this isn’t done by default is beyond me.