I developed a little Facebook canvas game with CSHTML5 (https://apps.facebook.com/bluemem). When I run it in Microsoft Edge or IE it works perfectly. In other browser (Firefox, Opera), it is not loading the classes when its integrated as a iframe in Facebook. When you just watch the iframe of the game it also works in Firefox and Opera.
Picture of Edge (it should work like this)
Same state in Firefox
Firefox (just the app iframe)