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.

works exactly as described, fixed the issue right away. thanks for making it!!