Persistent Spotify playlists across multiple browsers + devices

After successfully setting up my Pi Musicbox, I wanted to allow multiple users to add to the playlist through the web interface. I’m able to log several computers on at once, however, each computer has their own unique playlist.

Has anyone figured out how to make your playlists persist across multiple devices? Is there something I’m missing in the configuration?

Mopidy’s play queue is shared between all clients connected to that Mopidy server, but it is not persisted to the Spotify account that is used. There’s no built in way to sync the play queue between multiple Mopidy servers.