Almost Perfect Rated 4 out of 5 stars
I use this feature more than any other add-on. I strongly prefer a simple click for cloning tabs, rather than Firefox's built in [control+drag tab] gesture.
The other reviewers are right-on in praising its minimalism. In the past I've been forced to use tab utility add-ons bloated with extra junk I don't need. Keep it simple.
Only a couple things needed for a perfect 5 stars:
1) a tool bar button for 1-click cloning.
2) an option to open the cloned tab beside original .
A second context menu choice, Open New Tab beside the current one (instead of last-in-line) is also a feature I'd use a lot. But that might be bumping against the limits of single-purpose simplicity that make this add-on great. Maybe another choice under an "options" dialogue?
Then it would be perfect.