I've just installed the latest Ubuntu OS on my computer and when starting Firefox i get this problem while trying to play the latest YouTube videos where they say "Your browser does not currently recognize any of the video formats available. Click here to visit our frequently asked questions about HTML5 video." so I've tried to click on the link but then Firefox said my browser was already up to date. I've then tried to disable my adds on and try in safe mode but that did not help. I've tried installing some adds on, that didn't help either. I've tried uninstalling and installing back Firefox, that didn't work. every media.mediasource config are enabled, that didn't work. and when i try using another browser, the media can be played just fine (i used chromium). So if someone has any idea as to what might be causing this issue i'd be grateful (also, older video seems to be working just fine)