I don't have tbsync and I don't think any other extension I use added support for that. Simply select "On the Network" when adding a calendar, set a user name

I don't have tbsync and I don't think any other extension I use added support for that. Simply select "On the Network" when adding a calendar, set a user name and enter the remote dav location. For address books use "Add CardDAV Address Book", also username and dav location.