Firefox User agent no longer allowed?

[awfulshot]

This browser doesn't support Spotify Web Player. Switch browsers or download Spotify for your desktop.

I'm using Pale Moon with User Agent Mode set to Firefox Compatibility. This worked fine until today.

[casualfir]

You're right. I got the same problem today with my Firefox no longer allowed.

[CAJ69I]

Almost the same problem. I'm simply using the not default user, and I get the same error message. Firefox version is around 52.3, maybe, and I can't use the web player. Right now I'm paying for nothing! Good job, spotify...