Sadly all functionality is gone and this extension seems abandoned. The Last.fm site recommends using the extension called "Web Scrobble."

just doesn't work

This add-on is pretty well-designed but just DOESN'T SCROBBLE.

This extension doesn't work.

Doesn't work if the song/artist isn't already listed in a database, which is pretty dumb.

Claims to do the same as WebScrobbler, but doesn't do it. WebScrobbler is already a viable option for the purpose.