The obvious question...... . WTF do we need HTML5?!?!?!. Why HTML5?. . HTML 5 will enable better cross-browser compatibility and better support for Web 2.0-style' Web applications in addition to documents.". Brendan EichCTO, Mozilla. Why HTML5?. HTML5 will have an application cache that is capable of storing all resources in your Web app so that the browser can load them and use them even when you're offline.