What do you want from a "subfolder"? Thunderbird's Address Book supports Mailing Lists which ''look'' like subfolders, but a Mailing List can only contain Contacts held in its parent address book. The intent of Mailing Lists is that a List can be used as a portmanteau; its name stands in for all the contact addresses it contains, making mass mailings easier to set up. You can however create multiple independent address books, which can be useful to keep similar Contact types (e.g. personal vs business vs social groups) separate from each other. I have to warn you that Thunderbird's Address Book does not lend itself to easy use for other purposes. It is intended to manage all your email contacts, but doesn't offer tools for, for instance, creating address labels. I can't comment on your two other queries.