Created attachment 8872117 [details] aboutsupport.txt User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170527030204 Steps to reproduce: 1. In my normal profile, I tried to play a Amazon Prime Video 2. I got a message saying either I install Silverlight, or use HTML5 player on Chrome and Edge "Install the free Silverlight plug-in; it will just take a minute. Please refresh this page when the installation completes. If you have issues after installing, restart your browser and try again. If the issue persists, try using our new HTML5 video player on Chrome, Internet Explorer 11 on Windows 8.1 or later, Microsoft Edge or Opera. " Actual results: Unable to play video without silverlight Expected results: Nightly should be able to play with HTML5
Your about:support says you've turned off HTML5 media playback. You need to open about:config and change the pref media.mediasource.enabled to true. You've got a lot of add-ons installed... Maybe one you installed recently changed this pref?
Thanks, enabling that pref made the videos work. I have no idea why it was disabled in the first place. Resolving this as INVALID.
This also enabled 1080p video on Youtube for me. Earlier I was restricted to 720p.