Thanx for this. I actually created an account here, just to say a large "THANK YOU A LOT!" to MIXIT and other for posting this. I have spent many, many *hours* (an all nighter, actually, I must confess), trying to get a video I posted to my own website to actually render on my Firefox on my WinXP/SP3 box. The video renders successfully on my iPad, my Android tablets, and even my old Blackberry Playbooks - and it renders FINE in Chrome. But I could not get it to render on Firefox 47.0.1 at all, which I am running under WinXP/SP3. The detailed steps published in this thread let it work. Whoo hoo.
If curious, the video in question is an old Max Fleischer "Talkartoon" from 1932, called "The Robot". It's a charming example of early American anime, and speaks to what robotics and AI *should* aim to be, IMHO. When I tried to render in Firefox, it would *not* fall back to Flash, despite the latest Flash plugin being installed. Instead, it just failed with "No video with supported format and MIME type found." The suggestions and instructions were detailed and helpful. On the Youtube HTML5 test page, I get checkmarks in all the boxes now, for all video types. https://www<dot>youtube<dot>com/html5
And www<dot>quirksmode<dot>org / html5 / tests / video.html of "Big Buck Bunny" now renders in all three formats. Thanx again..!
Oh, my test video about the benefits of AI and robotics (circa 1932) is at: http://www.gemesyscanada.com/436569420
