This Add-On has been developed, to overcome the limitations of the Thunderbird e-mail lists, which do not sync very well via CardDAV, and have problems if a contact is part of more than one list.
This add-on scans all contact-cards of the currently selected addressbook, extracts all categories and displays a list inside the Thunderbird addressbook. It allows to rename and to remove a category (changes the category string in all member contact cards).
To be able to use this Add-On, you need to have a CardDAV-Server (e.g. SOGo, ownCloud, Baikal) and the SOGo-Connector Add-On needs to be installed (to hook at least one CardDAV adressbook into Thunderbird).