Even though Facebook's mobile Messenger specifically tells you that it tracks your location data the first time you install the app (and every time you start a new conversation), most folks don't realize how often and how accurately it actually does so. In fact, the app pings your location each time you send a text. And with this new Chrome extension, you'll be able to see exactly where your contacts have been messaging you from -- without their knowledge or consent.
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.