We're not sure what practical uses a waterproof fingerprint reader has—checking mail straight dripping wet from the shower maybe—but we rarely see eye-to-eye with the Japanese.
The device is waterproof and works exactly like a regular fingerprint reader, allowing you to authenticate yourself without a password. For the demo, their setup had a constant stream of water over the fingerprint reader, a situation most of us are in all the time. We'd gladly trade waterproofing for Firefox support.
The waterproof fingerprint reader [Akihabara News]