A new phone that runs Firefox OS is launching in Japan on Christmas Day, and it’s a looker. The Fx0 phone has an unusual feature that makes it stand out next to iPhones and Android devices: The Fx0’s exterior casing is transparent. The see-through phone is the product of a partnership between Mozilla and Japanese telecom giant KDDI. It’s the first Firefox OS phone to include features now commonplace among smartphones, such as 4G LTE and NFC, the technology used for mobile payment transactions.