Rated 1 out of 5 stars

No button. Nothing. But this is experimental so maybe down the road...

This review is for a previous version of the add-on (0.2). 

I tested with 102.8.0, and the button can be elusive. It seems to have problems with remote addressbooks, like CardDAV. When a remote update changes the displayed contact, the button goes away.
I should be able to detect that refresh and redisplay the button.