Gerv suggested extending the Firefox OS geolocation UX to include user-defined locations. For areas that MLS has no coverage, the user could still pick a location on a popup map (possibly guided by GeoIP). This user-defined location and visible wireless networks could be cached locally for later geolocation requests from the same location (e.g. home or work) or uploaded to MLS, tagged as "unreliable but better than nothing" data.
This feature could be extended to include geofencing notifications when the user enters or leaves their "Home" or "Work" locations.
Whoops! Should have added to Keyword.