Hello, I have been trying to figure this out for a few months and finally decided to see if anyone can help. Video's on twitter used to play, but for the past few months they have not played, just shown a blank square, after tying to get some help on twitter yesterday I noticed today that the blank square had been changed to actually say please use another browser. I usually use Waterfox, I have tried earlier versions of Waterfox, Firefox, new versions of both, I've tried the Developer Version of Firefox, and currently I'm using the Nightly build of Firefox, and they all will not play video's on twitter. I then found this page on Youtube https://www.youtube.com/html5/ which tells you what types of video the browser supports and then saw that Firefox does not support H.264 which doesn't make sense because the codec is installed in Firefox Plugins automatically. I am not sure what to do so Firefox plays twitter video's again, the same is true for my laptop, Firefox on it won't play twitter video's too. Adblock Plus is not installed, that was one of the first things I thought might be causing an issue.