The LG Fx0 sports a 4.7-inch screen with LG Display supplying the panel and comes with a transparent shell, run by Mozilla's web-centric mobile OS.

The device is powered by a Qualcomm Snapdragon 400 chipset with a 1.2 GHz quad-core CPU. It also has 1.5GB of RAM and 16GB of build-in storage space. The rear camera is 8 megapixel (MP) and the front 2.1 MP. The device features usual connectivity options and also comes with 4G LTE and NFC support.

LG did not reveal a detailed price but said it will be slightly higher than low-end models. It said the company currently does not have plans for releases in other countries.

LG released a Firefox smartphone that runs on the third-generation (3G) network in 2013 in the Brazilian market.

"We are very pleased to bring the first Firefox OS smartphone, based on Web technology standards, to the Japanese market today," stated Takashi Tanaka, President of KDDI on the Mozilla blog post.

"KDDI hopes to build the new era of the Web through Web of Things, enabling everyone to create custom connected Web experiences," he said.