In Firefox, if the about:config flag "media.autoplay.enabled" is set to false
then the spotify webplayer will NEVER work.
This flag is important to stop nasty web sites that bombard users with videos or ad-videos the user has no control over.
Please allow the web player to work correctly with this flag set to false.
I would have no problem with the music playing once I click play, but this flag stops a-hole sites that load a video without waiting for user to click play.