Our motto is "Mobilize Mozilla" and our goal is to change the web for another time in history. Firefox for Android and Firefox OS, are the new bleeding edge products for the new mobile web. Firefox OS simulator, Responsive design and a lot of new cool tools are the development tools that every mobile web developer must use. Thought this presentation I aim to help web developers to build and debug their web applications easy and fast. The web is the platform and the Firefox OS is key for creating a successful mobile web platform. That's why I am willing to present Firefox OS emulator, how to run web applications in it and especially how to debug them. Last but not least I am willing to present how you can debug Firefox OS (Gaia) which is HTML5, CSS3 and Javascript after all.