Sorry. Doesn't work.

I Used Tab Mix Plus before, where I could configure a shortcut for Clone Tab too. I got so used to it. I was so annoyed to right click a tab and click.
Now there is a solution! Thank you. The only problem is the shortcut. Alt + / is hard to reach on a german keyboard. Actually I have to use Alt + Shift + 7 to clone a tab.
Could you please make the shortcut configurable? From Tab Mix Plus I am used to Ctrl + Alt + T.
Yes, you are right that is similar to Alt + Shift + 7 :-). I just have to get used to it.

Great idea and super helpful, though I only wish he selected something more consistent with already existing tab shortcuts. Ctrl-T opens a new tab, Shift-Ctrl-T undoes tab close, it would have been neat to have something like Alt-T for duplication. OCD nitpicking aside, it's still great a add-on. Thanks so much!

Nope. Does not work

At least it works in a German version of Firefox with a German keyboard, but it is not pretty, because the combo is hard to reach.
Besides, an option would be nice to have the duplicate open in the fore- or background.