Building new Web APIs was a core pillar of Firefox OS development, and it applied to desktop Firefox as well. Unfortunately these efforts were bogged down by poor executive leadership and the difficulty of getting any other browser vendor to take new APIs seriously, so the work went pretty slowly.

Gamepad API spec efforts began as part of this, for example. Then another vendor kicked their own inferior spec out the door without talking to anyone and that ended up being the de-facto standard (not the first time). Other APIs like exposing battery status, network connectivity status, and the ability to notify with vibration were in the works, just to name a few I remember.