Dubbed the "Marauder's Map" (yes, like from Harry Potter), the extension leverages GPS data that's embedded into each Messenger message to surreptitiously locate and track whoever sent it. This isn't a real-time tracking method by any means, mind you; the extension simply compiles that embedded data into a cohesive map. However, it does allow anyone you've mailed with FB Messenger to see where you've been. If this sounds a bit too stalkerish for your tastes, you could always just uninstall Messenger and use any of the myriad of alternate texting apps currently on the market. Supposing that's not an option, you can alternately just turn off your GPS location service before launching the program.