Developer reply by Josh Geenen
Rated 2 out of 5 stars
I've used this add-on successfully for years on Thunderbird running on linux and really grown to depend on it. Unfortunately it seems to be broken now...hope it gets fixed
This review is for a previous version of the add-on (3.0.0).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.
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