The accuracy of Mozilla Location Service (MLS) has steadily declined. With no plans to restart the stumbler program or increase investments to MLS we have made the decision to retire the service. 

In 2013, Mozilla launched MLS as an open service to provide geolocation lookups based on publicly observable radio signals. The service received community submissions of GPS data from the open source MozStumbler Android app. In 2019, Skyhook Holdings, Inc contacted Mozilla and alleged that MLS infringed a number of its patents. We reached an agreement with Skyhook that avoided litigation. This required us to make changes to our MLS policies and made it difficult for us to invest in and expand MLS. In early 2021, we retired the MozStumbler program.

This is from their announcement regarding the sunsetting.