Adds a Close Tab (or Window, or Browser) button to the toolbar. This is especially handy if you put your tab bar at the bottom (i.e. with Tab Mix Plus) but want a Close Tab button in the top right, where you'd find it in most well behaved Windows programs with child windows. Once installed, just right click on the toolbar, select "Customize...", and drag the button wherever you like. The button's appearance is determined by the installed theme, and its behavior can be configured to close the current tab, window, or Firefox session.