Browsers have long contained development tools to help debug and diagnose problems when authoring Web content, but Mozilla is taking Firefox to the next level. Nightly builds of the browser now contain a development environment, WebIDE, for creating, testing, and deploying Firefox OS apps.
With WebIDE, developers will be able to create new applications from scratch, package them for distribution, deploy them to both the Firefox OS simulator and real Firefox OS hardware, and remotely debug them—all from within the browser and without the use of additional tools.
Read more at Ars Technica