It is now time to have a peek at Firefox OS. You can test your applications in two ways: either by running them on a real device, or by running them in Firefox OS Simulator. Let's go ahead with the latter option since you might not have a Firefox OS device yet. We will use WebIDE, which comes preinstalled with Firefox, to accomplish this task.
Note
If you haven't installed Firefox yet, you can do so from https://www.mozilla.org/en-US/firefox/new/.
WebIDE allows you to install one or several runtimes (different versions) together. You can use WebIDE to install different types of application, debug them using Firefox's Developer Tools Suite, and edit the applications/manifest by using the built-in source editor.
After you install Firefox, open WebIDE. You can open it by navigating to Tools | Web Developer | WebIDE. Let's now take a look at the following screenshot of WebIDE:
You will notice that on the top-right of the window, there is a Select Runtime option. When you click...