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Video playback not working correctly.

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Video playback is not working correctly on Windows 8.1 Pro and Firefox version 43.0.4. I've attached an error message I keep getting on YouTube. I get problems off and on playing video on Dallas Cowboys. com. MSN videos load very slowly and sometimes don't play at all. I've run them in safe mode so I don't think it is the extensions that I use. I have removed Ghostery and Adblock Plus. When I use Google Chrome all these sites load quickly, play with no errors even with Ghostery and Adblock Plus extensions running. What am I missing and how do I fix it?

Video playback is not working correctly on Windows 8.1 Pro and Firefox version 43.0.4. I've attached an error message I keep getting on YouTube. I get problems off and on playing video on Dallas Cowboys. com. MSN videos load very slowly and sometimes don't play at all. I've run them in safe mode so I don't think it is the extensions that I use. I have removed Ghostery and Adblock Plus. When I use Google Chrome all these sites load quickly, play with no errors even with Ghostery and Adblock Plus extensions running. What am I missing and how do I fix it?
Attached screenshots

الحل المُختار

I've called the big guys to help you. Good luck.

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1) Enter the config by typing about:config in the address bar. 2) Enter media.mediasource.webm.enabled and press enter. 3) Right click on it and change to true, for some reason it is set as "false" which makes MSE & WebM VP9 not work properly. 4) Visit: https://www.youtube.com/html5 and check that everything is OK. 5) Try to watch a video. It should work now.

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Thank you for your response. I have work through your steps twice and media.mediasource.webm.enable changed to true but the YouTube error still exists.

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الحل المُختار

I've called the big guys to help you. Good luck.

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Upon closer examination this morning I have found that MSE & WebM VP9 has a red exclamation point on https://www.youtube.com/html5. In your step 4 you asked to check https://www.youtube.com/html5 and make sure everything is OK. Seems like that is not OK.