CentOS 6.7 x64_86
Code:
$ uname -a
Linux localhost.localdomain 2.6.32-573.18.1.el6.x86_64 #1 SMP Tue Feb 9 22:46:17 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
Firefox ESR 38.7.0
Every video embedded in twitter has this message: "This browser does not support video playback."
I have flash loaded. But I have problems all the time.