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 (near-field communication), the technology used for mobile payment transactions.

In terms of specs, the phone isn't exactly remarkable, though it is a big step up from most Firefox OS phones. It has a 4.7-inch display, the same size as the iPhone 6, and also carries a 1.2 GHz quad-core processor and a relatively modest 2,370 mAh battery.

The phone was designed by Tokujin Yoshioka — who seems to have a thing for transparent phones. His brief was to embody the "openness, freedom and transparency" that Mozilla apparently wants to exhibit, according to a Mozilla blog post.

The Fx0 retails for 50,000 yen (about $420), which is a step up from Mozilla's $33 smartphone made for the developing world.

There are 16 phones that run Firefox OS, and they're available in 29 countries. No word on when or whether U.S. consumers will ever be able to get their hands on the Fx0.