I'm pretty happy with this extension that is doing what it should do (i.e. sync Thunderbird contacts with my zimbra email account). But its behavior in Thunderbird 16 then 17 is pretty uncertain and painful:
I rename one of my address books from "Foo Bar" to "Foo" (so 2 words -> 1 word) then suddenly (without any reboot from Thunderbird or so), this address book went nearly empty. No matter what I tried (mostly on the mab files), there was no way to restore it except re-import it through a CSV file.
The first time, it was ok. The second time it did it, I had no backup...
From now I treat this extension like a wild beast that can from time to time make some trouble.