media.mediasource.mp4.enabled
   media.windows-media-foundation.enabled (may not exist) "

''dupe of https://support.mozilla.org/en-US/questions/1086066'' Hi. I have a system with Windows XP. I have Firefox on it. The version is 41.0. I recently updated it. Youtube will only play videos at 360p. I installed the 'Youtube Flash Video Player' that allows me to change from Flash and HTML5. https://addons.mozilla.org/en-US/firefox/addon/youtube-flash-video-player/ a user called jscher2000 suggested this in another thread, I did this: "Could you check these preferences and see whether disabling them helps: (1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste media. and pause while the list is filtered (3) If either of these are set to true, try double-clicking to set them to false: media.mediasource.mp4.enabled media.windows-media-foundation.enabled (may not exist) " I have DivX Plus Web-player HTML5 plug-in but it is not signed and cannot be verified. I get this web-page: https://support.mozilla.org/en-US/kb/add-on-signing-in-firefox?as=u&utm_source=inproduct Should I update DivX and download the newest one into Windows? Or this is a Firefox plug-in and Windows XP issue? I go here: https://www.youtube.com/html5 In Windows Vista I can have all the boxes blue. But not XP. Is it possible in Windows XP?