Rated 1 out of 5 stars

Freezes up my Thunderbird so I have to exit and re-enter the program, I was disconnecting it and running it manually... that worked ONCE. Now it doesn't even sync anything anymore.

This review is for a previous version of the add-on (2.0.11). 

It shouldn't take more than a few seconds to sync a reasonable number of contacts (up to a few thousand). Were you synchronizing with a new address book or an existing one (like Personal Address Book)? Your address book could be corrupt, especially if you killed Thunderbird in the middle of a sync when it may have been writing to that address book. Try syncing with a new AB.