Mozilla Location Service (MLS) is an open, crowdsourced geolocation service based on publicly observable cell sites (and their cell IDs) and Wi-Fi access points (and their BSSIDs). The service is provided by Mozilla since 2013. Mozilla does not collect the SSID name (e.g. "Simpson-family-wifi") from WiFi networks, but collects the BSSID (which is often the MAC address of the WiFi device). To allow opt-out, Mozilla's client applications do not collect information about WiFi access points whose SSID is hidden or ends with the string "_nomap" (e.g. "Simpson-family-wifi_nomap").