If you recently updated your Flash player to version 11.3, you may be running into a compatibility problem. Does anything in this article help: Flash 11.3 doesn't load video in Firefox.

Thanks, but not a video problem (Songza is music only). I uninstalled Flash 11, but I still have no sound on my Firefox. But, sound is coming through OK on Internet Explorer...just as before. Thanks anyway

Songza uses Flash, at least on this page: http://songza.com/listen/a-michael-jackson-dance-party-TacticCo/

What version of Flash do you have at the moment? You can check for "Shockwave Flash" here:

orange Firefox button or classic Tools menu > Add-ons > Plugins