On some versions of FireFox there is an error when trying to view an mp4 loaded up on AWS from with the EdX video player.
The error on the screen is:
No playable video sources found.
The error in Firebug is:
HTTP "Content-Type" of "video/mp4" is not supported.
This apparently is a limitation of FF and so readthedocs should be updated with this limitation.
Load an mp4 up on AWS
Create an EdX video player component and link the mp4 to it
Try to play the video in Studio or LMS