Rated 2 out of 5 stars
To make this work, one must - somewhat contrary to the garbled instructions - use Thunderbird's 'customize' menu and, with that menu, drag the element called 'addressbook tab' to a toolbar. EDIT: Except, no, the pinned tab thereby created stops working after restarting Tbird. And . . I could go on. But, hold on, *is this addOn even MEANT to work with recent versions of Thunderbird?* If not, it would be better were it flagged as incompatible.
Thanks to the developer for providing functionality that Mozilla did not (but no kudos for the instructions and UI).