Sharing address books
From MozillaZine Knowledge Base
Copy the address book
One way to share address books is to store the user profiles on a file share and overwrite the addressbooks of each user with a simple "copy" command. However, this assumes all new entries or changes were in the copy thats being replicated. Its also error prone. You could avoid this by sharing a single copy.
The Addressbooks Synchronizer extension can copy address books from a local folder or file share, or use FTP , WebDAV, or IMAP to fetch the file. Its not a real synchronization tool, just an easier way to copy files.
Share an address book on a file share
Your personal address book is normally stored as a "abook.mab" file within the profile folder. This is specified in the prefs.js file. Early versions of Thunderbird let you replace the "abook.mab" filename with a full pathname to specify the address book was stored on a file share. That would let multiple users and/or machines use a single copy. However, that functionality no longer works.
If you're using Linux you could move a address book to another location (such as a file share) and then use a symlink to create a symbolic link to the file. As far as Thunderbird is concerned nothing has changed, the operating system hides the fact that the file is actually stored elsewhere. That works as long as you don't have a copy of the address book in the profile. The NTFS file system under Windows 2000 and XP supports an equivalent of a symlink called a junction point. It works fine with Thunderbird, but is too complex for most users.
Funambol and SyncML servers
Funambol servers are provided by some free online calendar services primarily to synch your your contacts and calendar with phones and PDA's. However, you can also use Thunderbird with them. Typically you can use either a Funambol extension such as the Funambol Mozilla Plugin or a SyncML extension such as the Tsync extension. You don't have to have a calendar (Lightning extension) if you just want to sync/share contacts.
Memotoo, Mobical, Mobyko, MyFUNAMBOL (its free but runs ads on some mobile phones) and Zyb are examples of free services running Funambol servers. Memotoo makes your contacts available using a LDAP server (directory server) . Thunderbird normally uses *.mab files to store an address book in your profile but it can also use a LDAP server as a address book.
See What if I have a BlackBerry device? for information about using a Blackberry with myFUNAMBOL. Search the list of supported phones of the other providers to see if they support it. Mobyko for example currently lists 57 specific Blackberry models it supports.
If the add-on doesn't support calendars
If you need to sync both a calendar and contacts and have problems finding a Funambol/SyncML add-on that supports syncing both contacts and calendars that will work with a free online service, consider not using Lightning and using Google Calendar Tab plus an add-on that just syncs contacts (either with a Funambol/SyncMNL server or with Google Contacts) instead.
Email provider specific add-on
There are a couple of email provider specific add-ons that synchronize Thunderbird's address book with your webmail address book. The Google Contacts and gcontactsync add-ons are examples of this. Search Mozilla Add-ons (AMO) to find others.
Some email providers provide synchronization programs (not add-ons) that will work with just their accounts. For example. Yahoo provides Yahoo AutoSync and Google provides Google Sync. Unfortunately, neither currently supports Thunderbird.
The ThunderSync add-on exports the contents of address books as vCards, and can synchronize them. The MoreFunctionsForAddressBook add-on also knows how to import and export vCards but it doesn't support synchronization.
Rather than using abook.mab to store the address book on your hard disk, you could use a LDAP server to share the address book. Unfortunately Thunderbird currently doesn't support editing entries on the LDAP server (this is bug 86405) so its most useful in an environment where an admin maintains a corporate address book.
The SoGo Connector extension adds support for remote DAV address books, and features that are meant to be used with the Lightning extension (a calendar). It supports GroupDAV , CardDAV and WebDAV Sync. The SoGo Integrator extension adds additional features such as remote administration of folder subscriptions, automatic propagation of updates to selected extensions from a local update server and automatic propagation of default settings that are useful when Thunderbird is used in an organization.
GCALDaemon: GMail contacts as pseudo-LDAP
This article describes how to autocomplete email addresses that you type when composing a message with email addresses from your Gmail address book, without having to keep your Thunderbird address book in synch with the Gmail address book. GCALDaemon has a built-in LDAP server that runs in the background to search your Gmail address book for addresses. It only supports autocompletion, you can't use it to access other other contact information or to modify any of the entries.
Unfortunately it uses a now deprecated GData API. The calendar synchronization is still functional, but the LDAP server doesn't sync with Gmail Contacts anymore.  Its not clear if Google Apps Directory Sync can be used to workaround this if you have a Google Apps account.
The SyncKolab extension synchronizes your contacts as well as events and todos (from the selected calendar) with a selected IMAP folder. You do not need a calendar if all you want to do is synchronize your address book. The extension prevents the display of the IMAP quota in the status bar. 
If you want to share the address book with other users you could use a public folder. IMAP supports the concept of public folders, though not every e-mail provider supports them.
Share the OSX System's Address Book
Thunderbird 3.0 (and later) can display the contents of the OSX System address book. The menu wording ("File -> Use Mac OS X Address Book") is misleading, Thunderbird can't modify the contents of that address book. This thread in the GetSatisfaction forum is used to post the latest information about its status.  
Integrate with a CRM
Thunderbird doesn't support Extended MAPI so integration with a customer relationship manager (CRM) frequently requires an extension written specifically for Thunderbird.
Mozilla Add-ons has:
Others solutions can be found via CRM to LDAP support, then connecting your Thunderbird on the LDAP. Some CRM does not provide in-house LDAP storage but you can find some plugins doing the job for you:
Some of the add-ons on the Mozilla Add-ons web site are experimental or only support Thunderbird 2.x. Sometimes if you disable version checking per Updating add-ons that will let you use it with later versions of Thunderbird. It depends upon what API's the extension calls.
Some CRM's such as Maximizer prefer to use Extended MAPI but can work with just SimpleMAPI support. In that case you will only see the Inbox in the Maximizer's E-mail window but it will also log what you send in the contacts Documents tab. The main problem relying upon Thunderbird's SimpleMAPI support is it is poorly supported (still buggy and incomplete). Its safe to rely upon it working with Microsoft Office applications, anything else is a calculated risk. It might break when you upgrade.
Another possibility is that it can be integrated via a Funambol server. This article describes how to Synchronize Opentaps and Mozilla Thunderbird.
If your CRM doesn't integrate with Thunderbird you might try configuring it to automatically BCC your dropbox address etc. so that outgoing and incoming emails appear on the contact timeline as this article about Pearl integration with Thunderbirddescribes.
Sync with a database
Hedera Contact Sync syncs address books with CouchDB. It currently supports Thunderbird 3.1 and has a status bar icon to show that that Hedera is loaded, an About dialog and a preferences dialog to allow you to toggle debug output to the Error Console at run time. 
Some versions of Linux install the Evolution Data Server to provide a global address book, calendar and task list for the desktop environment. The EDS Contact Integration add-on lets you use and edit those address book contents from Thunderbird.