Rated 5 out of 5 stars
The Tab Control add-on once had this feature, but it was removed. And even though FF now has a native duplicate tab function, there's no easy-click context menu for it. A cumbersome keyboard+mouse dragging procedure is required. So, this extension is very useful. Thanks for providing it!
(What an ordeal to post this review... signed up and verified using Firefox, and then it wouldn't let me log in with Firefox no matter what I tried. Had to log in with Opera.)