Rated 5 out of 5 stars

by R. Hansen on Oct. 28, 2018 ·

To make it work with Tbird 60.2.1, rename the xpi to zip. Open up install.rdf and change the Thunderbird max version to 60.*. Developer says it's only compatible before version 63, so if you're on beta channel, you're out of luck until it is maintained.

This review is for a previous version of the add-on (3.0.0). 

by Josh Geenen (Developer) on Dec. 4, 2018 ·

That works somewhat until TB version 63.0, then it will completely stop working. I'm tracking my progress towards supporting 63+ in https://github.com/jdgeenen/gcontactsync/issues/121. Thunderbird's rate of making breaking changes has outpaced my spare time, so your patience is appreciated.