Mozilla Location Service
Mozilla Location Service (MLS) is an open 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. In February 2019 MLS had collected more than 44.43 million unique cell networks and 1450 million unique WiFi networks (April 2018: 37.7 million UCN and 1145 million UWN, November 2016: 28 million UCN and 757 million UWN, November 2015: 17 million UCN and 427 million UWN). The mobile app "Mozilla Stumbler" for Android was available in the Google Play store from November  2014 to July 2018 and was also on F-Droid. Other F-Droid apps are also available for the same purpose. Mozilla does not collect the SSID name (e.g. "Simpson-family-wifi") from WiFi networks, but does collects the BSSID (which is often the MAC address of the WiFi device). The service is opt-out, meaning it will be enabled on client applications without the user's consent unless disabled. 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"). Mozilla publishes aggregated data  set of cell locations (MLS Cell Network Export Data) under a public domain license (CC-0). Unlike the cell database, the raw WiFi database is not made public because the underlying data contains personally identifiable information from both the users uploading data and from the owners of WiFi devices. However, Mozilla shares this proprietary data with its corporate partner Combain AB. Although the Mozilla Location Service is not used by default in Firefox, the service is used in the Vivaldi browser, and 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.