The KDDI Fx0 is the most powerful smartphone on the market, though its hardware is still a few notches down from rival flagship devices running Android or iOS. KDDI, a Japanese carrier, offers the phone only in Japan and gives it an appropriate lock screen. The phone has a 4.7-inch 1,280x720-pixel screen and 1.2GHz quad-core Qualcomm Snapdragon 400 processor.
The KDDI Fx0's home button features an understated Firefox logo. Developers haven't supported Firefox OS as much as some would like, but there are a number of apps. Those that run on the Web already, such as Microsoft's Outlook.com, are easiest to bring to Firefox OS.