How do I sync contacts with Mozilla Thunderbird?

sync.blue® dashboard

1. Create your free sync.blue® account here, if you do not already have one.
2. Create a new sync.blue® connection (source: as you like, target: "Mozilla Thunderbird").
3. Authorize the target "Mozilla Thunderbird" in Step 2/3 by entering a password.
4. Complete the setup of the sync.blue® connection (step 3/3). Click on "Save & Sync".
5. Wait up to 5 minutes until your contacts are available via CardDAV for Thunderbird.

Mozilla Thunderbird

1. Open the "Address Book".
2. Create a new "CardDAV address book" (File -> New -> CardDAV address book).
3. Enter the following access data:
   1. Username: sync.blue
   2. Address: https://carddav.sync.blue/PASSWORD/addressbook/
4. You will then be asked for further access data. Use here:
   1. Username: API_KEY
   2. Password: PASSWORD
5. The sync.blue® address book is now listed as "Addressbook" in the bar on the left saved. Now rename it (right click on "Addressbook" -> Properties):
   1. Address Book Name: sync.blue
   2. Synchronization: any, e.g. every 30 minutes