URL: https://m.youtube.com/
Browser / Version: Firefox Mobile (Tablet) 51.0
Operating System: Android 6.0.1
Problem type: Video doesn't play

Steps to Reproduce

my device is ASUS Zenpad3 8.0. (Z581KL)
but is embedded movie or movie site's movie is not play smooth well.
it is play slowly and sounds play juggy.
Firefox, Aurora too.
In Nexus9, it plays well.
ASUS support says "Firefox's problem".
please help me.

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