Developer reply by Philippe V.
Rated 1 out of 5 stars
if CardBook is active mailing lists don't show up in the contacts sidebar
This review is for a previous version of the add-on (26.7).by email please : cardbook.thunderbird@gmail.com
Edit : this was due to an incompatibility with an addon (for the moment unidentified)
To create your own collections, you must have a Mozilla Add-ons account.