Getting HTML5 error on many Youtube videos

[Sandow]

I have the exact problem. I didn't have media.windows-media-foundation.enabled so i created it and it didn't work.
I have Windows 10. Actually the problem started after fall update.

[James]

Are you using a N or KN version of Windows 10 ?

If so then you need to install a Media Feature Pack for codecs so HTML5 player will work in Firefox/SeaMonkey. You said you did a fall update as in a Windows update. Major Windows updates can sometimes make you have to reinstall this Media Feature Pack. You can test what you system supports before and after at https://www.youtube.com/html5

https://support.mozilla.org/en-US/kb/fi ... ox-windows

This was splited off of http://forums.mozillazine.org/viewtopic ... &t=3034545 in which it was posted by WinXP user which Microsoft does not support with this Media Feature Pack to fully use HTML5 player without workarounds. So your problem was not the same.

[Sandow]

You were right, it was Windows 10 issue. The solution was to install latest Media Feature Pack (https://www.microsoft.com/en-us/softwar ... eaturepack).
The interesting part was that they updated it only yesterday, because I did install it before with no result.
So sorry for bothering, it was Microsoft's fault.