Through brief reads in the forum I figured out that I've been selected to now use the open.spotify.com webplayer app. It simply doesn't function on Firefox, Windows 7 pro.
It won't play at all.
I've opened play.spotify.com on IE, and it's working. Phew.
I couldn't find how to report the issue to spotify directly, so I'm posting here in hopes spotify will see it and address the issue.