Hide VP9 support for Firefox. v0.2 2019-12-20
This script for Tampermonkey or Violentmonkey (not working in Greasemonkey) simply lies to YouTube and says that Firefox does not support the VP9 codec via MediaSource extensions.
It is uses a simplified version of the code in this extension which has more options (but also blocks VP8 which may be needed by some people):
https://addons.mozilla.org/firefox/addon/h264ify/
