Sony announced plans of developing Firefox OS based mobile phones with Telefonica, Sony has released an experimental ROM for Sony Xperia E. The ROM can be installed by developers, and Sony wants to gauge the progress made by the Firefox OS, and reach out to the them so that they can start developing applications for the OS.
Sony has the procedure to flash the experimental ROM on the Xperia E on one of its developer pages. To install the OS, developers need to unlock the boot loader of the phone and flash the ROM using a tool available on Sony’s Developer World website. They can switch back to Android using the same tool.
It’s worth pointing out that the experimental ROM doesn’t support radio connectivity available, so you won’t be able to make calls with the phone or connect via Wi-Fi or Bluetooth after flashing the ROM.