I’ve created a guide in order to help contributors better test their code using Firefox WebIDE.
Image may be NSFW.Clik here to view.

Firefox WebIDE runs a Firefox OS emulator which can help when developing to simulate how the application would function on a Firefox OS device. It also includes debugging tools which are helpful to developers.
The guide includes links to install Firefox nightly, screenshots to follow along with, and specific tips on installing the mobile webmaker app.
I am still waiting on approval, but you can view the pull request here. It is written using markdown and is best viewed as such.