After losing support for the official Pinboard extension in newer Firefox versions, I was looking for something that had all of the features I wanted without a bad interface. I've been using Pinboard Pin for several weeks now and it's really great! If you're reinstalling an old add-on that you've used before for Pinboard, give this one a try.
If you are looking for a Pinboard add-on that is compatible with Firefox 57+, you should definitely give Pinboard Pin a try! Works like a charm and the developer is really helpful, too. (In fact he has included my suggestions in his add-on within a few days. Thank you, Citole!)