As a longtime user of Thunderbird, I am very familiar with the Address Book. But a couple of years ago, "Cardbook" showed up on my Menu bar. It started out the same as the Address Book, but they are no longer identical. For example, in Cardbook my son's entry has one email address; in Address Book, he has four. What are the differences, and which one should I be using? This is of particular concern to me because I just synced my Address Books between devices using BirdieSync, and it wiped out a very important contact out of my Address Book. Luckily it was still there in the CardBook, but I don't want to lose my contacts in either.