Rated 1 out of 5 stars

by Juan M. Sosso on Oct. 16, 2015 ·

I just installed this extension. Because I was using an old extension to sync I already have a lot of Google contacts in my Thunderbird address book. I tell gContactSync to work in read only mode, only download from Google, when I do first time setup.
Now I have hundred of contacts duplicated in my Google account :(

This review is for a previous version of the add-on (2.0.7). 

by Josh Geenen (Developer) on Nov. 28, 2015 ·

Merge support is experimental, though it works pretty well if your contacts have names and e-mail address fields filled in. Could you e-mail me with more details?

In the meantime Gmail has an excellent tool for removing duplicates. If that doesn't work you can revert your contacts to before the dups were made and sync with an empty address book.

EDIT: Read-only mode applies only *after* the first sync. Otherwise your contacts from TB wouldn't be sent to Google during the initial sync.