In Firefox 29 center clicking at the top of a tab in a maximized window will open a previously closed tab instead of closing the tab you clicked

Middle-clicking a tab closes it, while middle-clicking an empty area of the tab bar opens a new tab. Different behavior is probably caused by a tab-related add-on like Tab Mix Plus. If you're not sure if you have such an add-on, restart Firefox with add-ons disabled and check if the problem still occurs. * [[Troubleshoot Firefox issues using Safe Mode]]