Description of problem:
On a RHEL 7.2 system I tried to play any of the files here:
No result, only silence.
Version-Release number of selected component (if applicable):
With Firefox 42.0 on Fedora Rawhide I can play the same files without problems. On Both systems I have the MATE Desktop but that shouldn't matter. Let me know what sort of debugging info you'd like me to provide.
Can you please retest with FF45?
I have the firefox-45.1.0-1.el7_2.x86_64 which doesn't experience this problem.
Help -> About Firefox says 38.7.0 not 45, is this expected or a bug? Let me know and I will file a separate BZ for it.