I have the exact same problem at
worldsbk.com beginning a week or so ago. Videos will not play, all I get is an unresponsive black video box with no error messages or anything. I figured out that the problem is the latest VDH because when I disable it, videos play fine again. Hope you fix this fast!!! I will keep VDH disabled for now. I don't care about downloading videos at this site (I have a membership), I just want to PLAY the videos and VDH is preventing this on the entire web site. I thought it had something to do with the latest Firefox update 46.0.1, but like I said, all works fine after VDH is disabled.