Firefox Os is a Linux kernel based Open-source OS for Smartphones and tablets. Firefox Os is Designed to Provide a Complete Community-based alternative system for mobile device using standards and approaches such as HTML5 application,Javascript and CSS. In this session of the mozilla web maker party, Reza Habibi talked about creating an app with HTML and Javascript. made a sample and Implemented it for Firefox OS. He explained the Manifest file Structure and talked about optimizing a HTML5 based app for Firefox OS, then he show the app on Firefox OS App manager and talked about running Firefox OS Simulator and Ported the app on it. He finished this session by talking about the developer hub and answering the questions.