I've been working on a project where I need to embed Soundcloud songs. Everything works if I try to open the page in Chrome, but in Firefox, it simply shows a gray box with the Soundcloud logo in the center.
I was trying to debug it, and here's what I see in Firebug. When I open the page, it says
TypeError: this.getFlashPlugin(...).match(...) is null
Error: Permission denied to access property "href"
After checking the network for some clues, it became apparent to me that the script wasn't being loaded at all. I started double checking everything and I noticed that the url from the working example did differ from yours not only by the url (https://jsfiddle.net and http://fiddle.jshell.net) but also by the protocol.
In the working example, the protocol was HTTP and so was the Soundcloud's API. However, your example was in a secured connection and the API's address wasn't. Which explains the "Permission denied to access property
Fortunately, Soundcloud provides a secured version of the API. I fixed your example by changing the protocol to HTTPS and it started working.
Change HTTP protocol