Android is one of many platforms that can run Open Web Apps. You need to install Firefox Aurora for Android (which is pre-beta) to access Open Web App capabilities at this time (September 2012).
There are no other special instructions for developing apps for Android. If you want your app to run well on Android, keep in mind that a smartphone is a small-screen device and it must be handled properly by your app if you want it to be usable on Android. A best practice for doing this is to use responsive Web design. [link http://en.wikipedia.org/wiki/Responsive_Web_Design]
There can be device APIs available on an Android smartphone that are not available on desktop OSes. For example, orientation, geolocation, vibration, and so on.
The apps developer documentation you find on MDN applies to apps that you want to develop for Android.
You can design an app to work best on a small device like a phone, or you can design one that will run well on all platforms.
- If you are developing apps for the Firfox OS and do not yet have a FFxOS device, a good choice is an app running on an Android phone.
- ? dev tools for FFxOS apps, what about using FF on Android? Wouldn't that be closer than a desktop browser with responsive design mode, if you didn't have a FFxOS phone to use?