1) If you close tab in Firefox and then click middle mouse button on white space besides tabs it reopens tab which you just closed. It also keeps history of tabs which you have closed so you can re-open more then one tab.
2) Also in Firefox (3) you have small dropdown list at the very right side of tab line where you can switch to any of open tabs. This could be an alternative and in my opinion better way how to implement this (-> http://sourceforge.net/tracker/index.php?func=detail&aid=1843000&group_id=95717&atid=612385\) feature request. A lot like what you see at "Window" menu.