Rated 3 out of 5 stars

Google-4-TbSync is a good add-on to use with this add-on. Provider CARDDAV CALDAV with Yahoo is not so good yet with TbSync.

This is looks as if it is going to be a very good add-on once it is working well. Unfortunately Google and Yahoo contacts support is not fully functional yet so CardBook, TbSync and Thunderbird CARDDAV address book do not work fully yet.

The best thing to do is export all your lists then import them to your email providers contacts one list at a time. Google handles merge duplicates and labels well. I use all three but with different email providers to see which turns out to work best.

https://engineering.andrew-lohmann.me.uk/windows-2-linux---operating-systems/linux-windows-maintenance#h.fkwlnkdyfb0o

This review is for a previous version of the add-on (3.0.1).