I am no longer able to play videos on Twitter, Facebook or other sites such as the UK's channel 4 on demand streaming service and BBC iPlayer. On twitter I get the same error described on this page: https://forums.guru3d.com/threads/firefox-will-not-play-videos-on-twitter.419952/ . See image 1 for the Browser Console log. On Facebook, if I click a video I just get a black video with the video duration shown as 0:00 (as thought the video has not loaded). On the UK's channel 4 service I get an error message saying, "Digital Rights Management (DRM) Not Enabled. You must enable DRM in Firefox to play video on channel4.com. Click the "Enable DRM" button provided above". However the Widevine plugin is present on Firefox and is set to "always activate". See image 2 for the Browser Console log. On BBC iPlayer, I get an error message saying, "The content doesn't seem to be working. Please try again later". See image 3 for the Browser Console log. When I go to https://www.youtube.com/html5 "H.264" and "MSE & H.264" are shown as red exclamation marks. I have tried the solutions mentioned on the web (such as clearing cache, turning off content blocking, clearing cookies & site data, creating new profile, refreshing Firefox, uninstalling Firefox (including from the registry) and reinstalling, etc) and nothing has worked. These issues are not resolved by opening Firefox in Safe Mode. Any assistance would be greatly appreciated. Thank you!