Review for Contacts Sidebar by janffm
Rated 5 out of 5 stars
The original "Contacts Sidebar" does not work anymore on TB 52. There is a new similar addon called "Custom Address Sidebar" with the same functions!
https://addons.mozilla.org/de/thunderbird/addon/custom-address-sidebar/
To create your own collections, you must have a Mozilla Add-ons account.