Firefox OS is one of the emerging platforms in the market, with devices having been released in a large number of countries. Developing applications for Firefox OS is very easy, especially for web developers, as Firefox OS treats HTML5 applications as first-class citizens, and hence there isn't any requirement to learn about using any unique platform-specific SDK.

The greatest thing about developing applications for Firefox OS is that the apps that you construct can run on a host of other devices that run Firefox as well, the goal being to make the Firefox OS apps to run in any web browser. For example, if the application that you build is responsive, then you will also be able to install and run it on a computer/laptop that runs Firefox. Isn't that great? Firefox is available for Windows, OS X, Linux, and Android, and very soon it will be available for iOS as well! This will allow you to distribute your applications to a wide number of people using different platforms. Also, unlike platforms such as iOS, you are not forced to publish your applications via the official marketplace; you can host your applications by yourself as well.

Mozilla has a huge community of developers and users, who are always willing to help others on platforms such as GitHub and IRC (https://wiki.mozilla.org/IRC). Firefox OS also has a great marketplace, which has grown over the years and offers great applications. Even the user interface of Firefox OS, which is known as Gaia, is built with the help of three components, namely HTML5, JavaScript, and CSS3. This makes developing applications for this platform easy for people who have experience in web development.

You can also port the applications that you build for Firefox OS to native applications for other platforms with the use of software such as PhoneGap, since Firefox OS applications are essentially web applications.