4.1.4 CardBook

CardBook is an awesome complete and well-tested Thunderbird extension implementing many features missing from the default Thunderbird address book (that will actually get reworked soon).

Although, there will be a glitch against Thunderbird v68+ if you use this thunderbird user.js as long as remote CardDAV synchronization.
You'll have to relax network.cookie.cookieBehavior from 2 to 1 (see preference 2701).

For further information, see this page.