Rated 1 out of 5 stars

It deleted all of my contacts (except for 38 out of 186) from my Gmail contacts folder.

I guess I should have made a more recent backup but I just didn't believe that it could possibly go that wrong. Luckily I have my google contacts backup from my phone to fall back on.

One star for actually syncing the contacts to thunderbird before deleting them all.

This review is for a previous version of the add-on (0.8.13). 

There are no outstanding bugs that match what you describe..

The addon is a full two-way sync, so if:
a. you are in sync
b. you delete contacts on one side
then
c. the addon will delete the corresponding contacts on the other

If you feel that the addon has behaved incorrectly, please file a bug report:
http://zindus.com/i/reporting-bugs