Looks like Unity Web Player is not supported on your system. You can try standalone versions from the game description page or WebGL (HTML5) version.
Mouse — swipe to throw fireball.
Mouse (hold) — press and hold to cast pyroblast.
Esc — back / pause.
Unity Web Player is not supported on most browsers for now. Try other web browser (for example Firefox)
If still not working try WebGL (HTML5) version.