Mozilla Location Service (MLS) was an open geolocation service that allowed devices to find their position by processing received signals of publicly observable radio transmitters: cellular network antennae (and their Cell IDs), Wi-Fi access points (and their BSSIDs), and Bluetooth beacons.

[9] The mobile app Mozilla Stumbler for Android could be used to contribute signals of cellular networks and Wi-Fi access points at the device's GPS position.

Mozilla's client applications do not collect information about WiFi access points whose SSID is hidden or ends with the string "_nomap" (e.g.

[18] When the service is used to request the geolocation of a device by sending it information about nearby radio transmitters, it not only responds with a location estimate, but also uses the data to update its own database.

These requests are also used to verify that the 5 reported Wi-Fi networks still exist, and that their characteristics, such as their location, orientation, or other factors that might alter the signal, are unchanged.

If they are changed, for example, by someone moving their Wi-Fi router to another room, then the device gets the Blocked status, which means that it isn't taken into account for location queries for 48 hours.

This is used to filter out, for example, Wi-Fi access points on buses and trains, and mobile hotspots created by phones and laptops.

[25] It is also the primary location source in the GeoClue library for non-GPS enabled devices, which is used in the GNOME and KDE environment in location-dependent applications such as the ones providing weather and maps.