You can drag and drop from one address book to another. There is nothing in Thunderbird called a "contact list". It has address books and in them you can create Mailing Lists, analogous to Distribution Lists in other email clients. A Mailing List ''looks like'' a subfolder of an address book. It forms a group of contacts that you might want to email collectively, such as members of a club. It is a sub-set of the address book it belongs to, and can only contain contacts who exist in its parent address book. If you try to add new contacts directly to a Mailing List, those contacts will also be added to the List's parent address book.