YouTube wanted to deprecate Flash video, so Mozilla enabled VP9 support in Firefox 43 for users whose operating system does not provide an H.264 codec. (VP9 for all other platforms is coming a little later.) YouTube disabled Flash for Firefox 43 users, as planned, but forgot (?) to enable VP9 for those users. Without H.264 or Flash video, those users received low-quality 360p VP8 instead of high-quality VP9. When this mistake was discovered, YouTube could not fix or revert the configuration change because of their holiday code freeze.<p>(I am a Mozilla employee.)