After a couple of hours playing spotify with firefox, firefox is sucking 2gb+ of memory, and it just gets worse with more usage. I know it's spotify because I downloaded an addon that says which tab is using the memory.
I have a similar issue, only it goes up to 3GB + within 20 minutes or so of use on large playlists (In particular the 170+ song Coachella 2016 playlist). I can't enjoy music anymore because I have to force-kill the firefox process to free the memory every 20 minutes. I'm using linux with firefox, if that makes a difference.