Trying to play Widevine with no Windows Media Foundation (nor Silverlight fallback), see https://support.mozilla.org/kb/fix-video-audio-problems-firefox-windows
尝试在无 Windows Media Foundation（也无 Silverlight 后备）的情况下播放 Widevine，参见 https://support.mozilla.org/kb/fix-video-audio-problems-firefox-windows