Rated 3 out of 5 stars
TB sync with icloud works first time syncing and then stops.
Why? No idea. Both test-computers did only populate the first time and then we had to uncheck the sync for the contacts.
Recheck the contacts field and it was syncing again.
The syncing after the initial sync is not working with Thunderbird 60
I cannot confirm this. Please open a bug report (under help in the TbSync Account Manager) or contact me via email directly.