To be clear, I'm talking about the functionally asserted here: https://support.mozilla.org/en-US/kb/switching-thunderbird#w_importing-the-os-x-address-book That simply doesn't happen for me, and I have no idea where to go looking for what's causing the problem. I'm aware of this old post: https://support.mozilla.org/en-US/questions/1096840, and Thunderbird does successfully request permission to Contacts when first run, and I do still have it granted (see attached screenshot). Update (2016-12-03): I think this may be related to some sort of iCloud/sync misbehavior or corruption, not explicitly Thunderbird, although I'm seeing it on more than one computer with the same OS, and I'm not having problems with other applications that try to use the Mac OS X Address Book, so that seems strange. When I start Thunderbird from a command line directly (as `/Applications/Thunderbird.app/Contents/MacOS/thunderbird-bin`), I get these messages on STDERR (it seems like nothing about Address Book interactions is logged to $NSPR_LOG_FILE, even with NSPR_LOG_MODULES=imap:5,smtp:5,pop3:5,ldap:5,ImapAutoSync:5,MSGDB:5,times tamp … is there an additional module that relates to the Address Book interaction?): 2016-12-03 10:18:54.612 thunderbird-bin[74414:4205316] [Accounts] Failed to update account with identifier 04C0271C-498C-40E2-8057-37E1FAB7067D, error: Error Domain=ABAddressBookErrorDomain Code=1002 "(null)" 2016-12-03 10:18:54.627 thunderbird-bin[74414:4205371] [Accounts] Failed to update account with identifier 91062920-1016-4701-91DC-36A69F3D8ED3, error: Error Domain=ABAddressBookErrorDomain Code=1002 "(null)" The Google hits for that error message at sources I trust are not promising: https://forums.developer.apple.com/thread/21089 http://apple.stackexchange.com/questions/216933/contacts-app-failed-to-update-account ... and the promising sources are wishy-washy (and only mention this particular error message in passing): https://discussions.apple.com/thread/7302886?start=0&tstart=0 I do think this has something to do with synchronization, but I'm not sure it's iCloud-specific. When I tried to open the iCloud System Preference pane, I initially got the rather unhelpful modal dialog, "Preferences Error: There was an error in iCloud preferences", and needed to re-supply my Apple ID login info, but that eventually behaved. Just doing that was not enough to make "Mac OS X Address Book" show up in Thunderbird, and the same error messages show up in STDERR. Next I went into the "Internet Accounts" System Preference pane and disabled Contacts synchronization with both iCloud and an Exchange (for work) account. At this point, I can start Thunderbird and "Mac OS X Address Book" DOES show up... and the same "Error Domain=ABAddressBookErrorDomain Code=1002" errors appear on STDERR. So... I'm not sure those errors are actually related to my problem. Next I re-activated first the Exchange Contacts link in Internet Options, and that led to having no "Mac OS X Address Book" show up in Thunderbird. I turned that back off, and reactivated the iCloud Contacts link in Internet Options, and I do now see "Mac OS X Address Book". So I think the actual bug here is that Thunderbird somehow fails to parse Contacts from Exchange, and dies completely rather than just leaving those out. This partially fixes my problem, and not having access to Exchange directory services in Thunderbird isn't a huge deal, but I'd prefer to still have it elsewhere. Is this "fail silently when reading Exchange Address Book information" a known problem?