User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0 Build ID: 20150402191859 Steps to reproduce: Nothing. Just updated to 37.0.1. Actual results: YT-Videos stopped working. No plugin is active. Expected results: Videos should play in HTML5. Switching media.mediasource to "false" resolves it. Not a permanent solution I guess.
Hardware acc is OFF and GPU is NVidia GTX 760, driver ver 344.75.
Could you test YT videos with a fresh profile, please. https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
Done. With fresh profile YT videos work. I usually have no plugins installed and as addons "adblock plus,noscript,flash video downloader,proxtube. I found the reason: It's noscript. It blocks mediasource (that's new). One time disabling NS and re-enabling + allowing mediasource as script does it. You can mark this bug as solved if you wish.