Firefox/Mozilla is able to retrieve your current location by sending some local data to a 3rd party service. In return the browser is informed about your current position.
When using this add-on no commercial service is used for this kind of geolocation but the free OpenWLANMap project. Please find more details at http://www.openwlanmap.org
Both services difference in two major points:
- Google provides a commercial service (although it is available for free it is) while the OpenWLANMap project does not have any commercial interests or an advert-driven income
- Google does not offer a possibility to put the own WLAN network out of the list while you can delete it out of the database of the OpenWLANMap project - there the owner of a WLAN can decide if a network shall be listed and used for geolocation or not