I don't know definitively what the file names are but, in the root: C:\Users\[User name]\AppData\Roaming\Thunderbird\Profiles\[release file] are files that begin 'abook' and, having opened them in Notepad, I've searched and found some of my contacts. So, I'm guessing that all these are the Address Books. However, make sure you remove and save all of the existing files to a folder on your Desktop before moving the old ones in so that you can restore them if there's a problem.