У вашего броузера проблема в совместимости с HTML5
http://www.wolfire.com/overgrowth
A demonstration of Overgrowth's map editor system. Learn how to use Overgrowth's built-in tools to arrange complex scenes. Watch Rabbot navigate a custom-made environment. Finally, see how all the map editor tools can be used together to build a complex structure. Be sure to keep up with the latest development news at the Wolfire Blog: http://blog.wolfire.com/