Mozilla's Thunderbird lacks native carddav support; that's been an issue for years now, with no plans on deck anytime soon.
For awhile, the Zindus plug-in ( https://addons.mozilla.org/en-US/thunderbird/addon/zindus/?src ="ss") provided a Sync-TBird-to-Zimbra solution. Unfortunately, that plugin's no longer functional or supported.
As Zextras' zxmobile is an activesync-compatible provider, activesync is an option ...
SoGo's 'Connector' Thunderbird extension (SOGo: Frontends) works over ActiveSync, but only for old versions of TBird.
There IS one activesync client available for TBird that's currently being developed, and works well with a number of ActiveSync providers: tzpush
https://addons.mozilla.org/en-US/thunderbird/addon/tzpush/
I've attempted to connect tzpush to a ZXMobile-enabled ZImbra instance.
I see the Thunderbird 'device' registered in the ZXMobile admin UI.
Unfortunately, on exec of 'sync', there are no contacts transferred at all.
I've verified that it works as advertised with both Zarafa & Horde. It does not seem to work with Zimbra/ZXMobile.
Thunderbird is a widely used client. Lack of network addressbook/contact sync is a blocker to adoption of Zimbra/ZXMobile.
Has tzpush functionality been demonstrated for sync to/from ZXMobile?
If not, it'd be useful -- to both existing ZXMobile installs, AND to potential/new ones -- if there might be some outreach/communication from Zextras with the tzpush developer (who seems to be quite responsive ...).