Some snippets target specific countries. For example a snippet about a greek national holiday would target only browsers requesting snippets from Greece.
To preserve user’s privacy the geolocation happens on the browser level and not on the service level. Snippet bundles contain a list of targeted countries among the actual snippet data, the snippet weight and other info.
The Browser pings Mozilla Location Service (MLS) to convert it’s IP to a country code. Upon successful response the result is cached for 30 days. Thus if a user travels from Greece to Italy for a week snippets targeting Greece will be shown while the user is in Italy.
The GeoTargeting code is part of the JS included in the snippet bundle and it’s managed from the snippets service itself. It is not part of Firefox.