"In order to express the openness which is the most distinctive feature of Firefox OS, Tokujin captured the beauty of mechanicals inside and incorporated them to the design," said a statement from the designer's studio.
Mechanical parts within the case give a metallic appearance to the design, which is textured across the back to improve grip.
The phone features 4G capabilities – one of the first for a Firefox operating system (OS) device – and a quad-core processor produced by Qualcomm.
A large touch screen covers the majority of the phone's front, while a camera is mounted within a black disk on the back, with the flash located just below.
Firefox's logo is on the circular "home" button "to identify the originality through the front design of the body".
"This will be a model that symbolises a new stage for Firefox OS smartphone," said Yoshioka, who also designed another transparent phone for KDDI called X-RAY in 2010 and launched his Media Skin mobile phone with the brand in 2007.