It's not required. Perhaps Firefox's implementation of privacy blocking breaks the behavior of the API, which has a standard way of denying location information. Or maybe you're also blocking the IP geolocation service that I use as a fallback.

Just following up, I tested in Firefox with strict privacy settings and location disabled, and it works for me with the IP geolocation fallback. If IP geolocation fails I have a further fallback to enter your street address. So something else must be broken.