The web-as-app approach doesn't work particularly well when you're trying to deliver a rich and smooth experience, especially on mobile.

ENGADGET: Firefox OS is repeating the mistakes of others and hoping for a different outcome

Ultimately the web-as-app approach doesn't work particularly well when you're trying to deliver a rich and smooth experience, especially on mobile.

ENGADGET: Firefox OS is repeating the mistakes of others and hoping for a different outcome

Compared with an HTML5 mobile app, which can be developed once and run on many different platforms, a native app approach can be significantly more expensive, since these apps must be developed platform-by-platform.

FORBES: HTML5 Vs. Native Mobile Apps: Myths and Misconceptions