Review for Duplicate Contact Manager by Translucide
Rated 5 out of 5 stars
This extension works well and works with TB 45.
However, it has a bug: if "All Address Books" is selected, if does not work as expected (dialog show up but does not let you select which addess books you want to compare.
You have to click on an address book first, then it will display its main extension dialog properly.
To create your own collections, you must have a Mozilla Add-ons account.