I have an issue when I play some videos in Firefox with html5 tag : I can see well the images but the sound is ~6,5sec delayed ! These videos have been made via a mobile app, so maybe something is missing in the header file or something like that. I'm using Firefox v47.0, with Windows, but it happens on Mac Os (v47.0 too). I tried on several computer with same version, same issue. But everything seems to be ok on Firefox v40. I tried without any add-ons, disabling hardware acceleration, same thing. It works perfectly with other browser. So is there any change about video between these version ? What can I do to avoid this trouble ? Thanks for help :)