By the restriction of Spotify, this add-on only works with Spotify premium account. Spotify has a really cool feature called Spotify Connect. Basically it could turn anything into a Spotify player, and control it with your cellphone. I made this app trying to connect Spotify with Firefox. So why use this player instead of Spotify website?

Play in background of Firefox, no need to keep Spotify's tab open;
Keyboard shortcut to play/stop/next/previous/save;
Transfer playback to this player seamlessly with just one click.

After install it from the web store, use it in the following steps:

Authorize on Spotify;
Enable autoplay permission;
Choose music on Spotify and play it on "Spotify on Firefox". If you have a premium account on Spotify, you can seamlessly transfer your playback to this player, with just one click on the play button.

Besides, it's open source! https://github.com/revir/spotify-on-browser Read more: https://revir.github.io/2021/01/16/Spotify-on-Chrome/ Feedback can also be here: https://pnl.dev/category/3/feedback

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