The W3C defined a generic sensor API for browsers which also allows to support sensors like the Magnetometer. The spec can be found here: https://www.w3.org/TR/generic-sensor/
Does Mozilla intend to support that API for Firefox? Is it maybe already under development?
(note: Chrome 63 does support it in it early version already)
Usually it’s also a good idea to look into Bugzilla and do a search to see if there’s something filed - if you have an account, you can follow a bug that may already be filed or create a new one to track it (they can WONTFIX it but then it’s at least documented that there’s no intent to do it). If there is a bug though, do not post “me too” comments, just follow the bug.