Earlier this month Mozilla announced it is renaming its Boot to Gecko operating system for smartphones to Firefox OS while touting support from major carriers worldwide. Although the first Firefox OS-powered devices aren't expected to arrive until sometime in 2013, Mozilla's engineering team has begun posting nightly desktop builds of Firefox OS online for anyone to play with on their computers.
The builds provide an x86 Firefox OS runtime compatible with all major PC platforms – OS X, Windows and Linux – and can't be sent to a phone or tablet. The idea is for the project's contributors to test the Gaia shell and applications that are built for the platform, as well as giving early access to third party developers who might want to start building applications that are compatible with Firefox OS.
As reported earlier, Mozilla's mobile operating system is entirely open source and built with standards-based web technologies such as HTML5 and CSS, making it extremely customizable.
Looking at early screenshots and demo videos the Firefox OS interface resembles Android and iOS, offering typical functions like calling, texting, calendar, contacts and more though a grid of icons. That said, it's important to note that this is still a work in progress and the nightly builds may not necessarily be indicative yet of what the final user experience will be like.