Thunderbird Extensions Found To Work With Postbox
While a fork of Thunderbird there is no guarantee that extensions created for it will work with Postbox, it is more a case of trial and error.
The following are ones that have been found to be compatible with Postbox 4.0.3:
Failure Of MAC OS X Contacts (Address Book) Integration
This traces back to a value not being written to the configuration file after authentication Thunderbird in System Preferences | Security and Privacy |
|Value:||Mac OS X Address Book|
Thanks to Metaparadigma, which while not the actual solution above pointed me in the correct direction.