Holy s***, I love you Asecave... For years my SoundCloud has been broken on Firefox. My previous best solution involved clearing the cache and having to log-in, complete capthca again. This has worked perfectly so far. I'm very surpised there is no official solution but for now ily Asecave <3

Works perfectly for SoundCloud, but another fix is to go to about:config and turn dom.ServiceWorkers.enabled to false.

Reddit post where I was told of this fix:
https://www.reddit.com/r/firefox/comments/18z303j/comment/kgkhixo/?context=3

I also posted on the Bugzilla so they're aware of this.