Having the same experience as others. Ever since the update, it no longer works. It opens up the extension to pin the image but there are no boards available. It is empty. Only has the option to 'create board' but even if you do that it errors out. Definitely logged in to Pinterest in the browser. If you navigate to a site that has a 'pinit' action embedded on the image and use that it works fine (as normal). It is purely the browser extension that is no longer working (whether from the browser button or the browser added Pin save button overlay on images). Open the pin image showing empty with no boards to choose from and no ability to pin.

Have disabled all extensions = same error.
Cleared cache = same error.
Restarted computer = same error.Private browser (is allowed in there) = same error.
Disabled the extension and reinstalled multiple times = same error.

Running FF Developer Edition 68.0b8.
Pin version 4.0.82
Mac Sierra 10.12.6
Logged into multiple Pinterest accounts.

Thanks!