У вашего броузера проблема в совместимости с HTML5
SFML, Simple & Fast Multimedia Library, just released version 2.5.0. SFML is an open source C++ framework providing low level functionality like windowing, networking, 2D graphics, input and more. This video takes a very quick look at the new functionality in this release.
For more details of this release check out:
http://www.gamefromscratch.com/post/2018/05/12/SFML-250-Released.aspx