Rated 3 out of 5 stars

Very good and useful tool! Why 3 stars? Because during the sync Thunberdird freezes!!! Can you resolve it?

This review is for a previous version of the add-on (0.3.0). 

Thanks for Your review.

Yes, Google-4-TbSync is still in its early releases, and this is one of the issues.
I think it could be circumvented by using the "workers". But this would be a major rewrite of the code, and I'm waiting for another one to happen first (i.e. migrating to the WebExtensions API).

Eventually, it will be fixed and synchronizations will be possible in the background. But I can't tell You when.

In the meanwhile, You can speed things up a little by unchecking the "Include system contact groups" and "Use verbose logging" options.

Thanks,
MZ