I needed a replacement for Sogo Connector, which I used with an older fork of Thunderbird. This addon along with TBsync completely replaces the old connector, and works like a charm with Thunderbird 60. I'm able to sync my calendar and contacts.
Initially there were some problems, it did not properly cooperate with my Radicale server, but thanks to the authors helpful attitude, the issues were fixed lightning fast :)
If I could, I'd add 10 stars.