Review for Duplicate Tab Blocker by Alice
Rated 3 out of 5 stars
It does the job of preventing you from opening duplicate tabs, although giving us the option of the addon making the duplicate active or not would be nice. And on top of that the addon conflicts with another of my addons, I believe TabMix Plus, preventing TMP's session manager from working at all and even causing Firefox to close without any errors.
To create your own collections, you must have a Mozilla Add-ons account.