Since Firefox 3.5, move a tab in the tab bar using the keyboard became a problem. You must have the focus on the tab bar in order to make the shortcuts Ctrl Left and *Ctrl Right work, and click is not enough. To do so, the easiest way is Ctrl k to focus the search toolbar then Tab to focus the tab bar. This "solution" is just a work around, and a little bit too complicated to only move a simple tab.
Move Tabs is a Firefox addon designed to enable you to choose your own shortcuts to move tabs around. You can move the tabs along the tab bar and at both ends.
Requirements:
· Firefox 3.5 - 13.0a1