Facebook has switched to HTML5 from a Flash-based video player for all Facebook web video surfaces, including videos in News Feed, on Pages, and in the Facebook embedded video player. Facebook explains the benefits of HTML5 that they will be using: development velocity, accessibility features, and page load time regression. Facebook: “We are big supporters of the HTML5 since it eliminates the weakest link in the user environment and in terms of development, it makes the job easier for developers.”]
Source: http://securityaffairs.co/wordpress/42937/social-networks/facebook-stitches-flash-html5.html