I install Mozilla Thunderbird into a large number of computers (replacing other mail programs). LDAP does not meet the requirements: can not get the address book in
the offline, can not immediately see the entire email address book (this requires the employer).

Once upon a time I wrote a email to the author extension — Günter Gersdorf:

«Is it possible to add to Addressbooks Synchronizer the following function.
— Addressbooks Synchronizer (on user computer) receives the address book in file in LDIF format (from network share)
— and force makes Thunderbird (on user computer) to import address books automatically

To which I received a reply:
« Please download and install AddressbooksSync-0.9.7_a1.xpi
To access the new functionality, open the options dialog of Addressbooks Synchronizer. Rightclick on the addressbook you want to be loaded from the LDIF file. Enter the filename of the ldif file. Only enter the filename, as the location is defined on the right side of this panel. The filename must end with ‘.ldif’»

Now in version AddressbooksSync-0.9.7_a2, AddressbooksSync-0.9.8, this feature works great!

I think this feature raises the Addressbooks Synchronizer to  level of enterprise solutions.