While you still cannot get a Firefox phone yet, because there is still a long way till a device will be ready, you can get your hands on their mobile platform and try it out right now.
Mozilla has recently started sending out the nightly builds of their mobile platform on to their FTP servers. The platform, called Firefox OS, is a mobile operating system that is aligned with standards-based Web technologies. Based on the Gecko HTML rendering engine, the software is built on the Linux kernel and a user interface called Gaia. It was first announced in 2011 under the former name Boot 2 Gecko (B2G). Since the initial announcement, the platform had some time to mature and grow to be able to be released to computers.
Mozilla’s Tony Chung said on his blog
We’ve been culturally challenged to build up a interested community of testers, but limited to our distribution of builds due to legal contracts. However, the release engineering team was able to get Daily desktop builds created and published online for anyone to play with.
The builds right now are x86-compatible Boot 2 Gecko runtime using the Gaia shell. As of right now, there are some applications on the device that are built for the platform. Though you will need to do a little bit of configuration to get the program ready, like obtaining the latest Gaia code from the GitHub repository and generate a profile to use in the environment, this will be a useful tool for third-party developers who want to start building applications that are compatible with the platform, not to also mention a great time for Gaia contributors.