hi sandstorm, your ip is part of the networking protocol and necessarily gets transmitted to every page you visit for that reason - what you have seen is probably a prompt triggered by the geolocation API that the website was requesting. your exact location is not stored within the browser but is "calculated" on the fly by basically using the list of wifi networks that are in the range of your device to get an approximate location.

https://www.mozilla.org/en-us/firefox/geolocation/

IP can give a rough estimate, sure, but are you sure that IP can give my exact home address to websites that request that?

no, that was not what i was saying. your ip address is known by websites by the virtue of you communicating with them and doesn't have to be requested (and yes, that piece of information will only allow an estimate of your location).

the prompt that you have seen was something different, namely a prompt to allow the geolocation api to provide the site with a more exact location. this is how it works in principle in simplified terms: your device sends a list of all wifi networks it sees within range to a google service - they know where those wifis would be placed in the real world, because they drove by in the past with a google car recording the whole radio landscape and mapping it to gps data. so by knowing which wifis are sending around you, they can triangulate your location and firefox will then submit that to the requesting website...

Now how can we spoof that info on demand?

you could try if an addon like https://addons.mozilla.org/firefox/addon/location-guard/ helps.