Hi, I’ve searched and found some questions but no answers about syncing the contacts through CardDAV protocol with Thunderbird.
This isn’t a core feature of Thunderbird, but can be achieved quite simply and seamlessly with a small Thunderbird plugin: https://addons.mozilla.org/en-GB/thunderbird/addon/cardbook
Have fun syncing, and go on degoogling your life!
(as a side note, as a first-time-poster, I’d like to thank the developers of Mail in a Box for an amazing product that is really and truly empowering for its users. Thank you so much!).