Geolocation

Geolocation API Specification in W3C
Geolocation API - Gears API
Google Gears also provide this feature for Android 1.x device or emulator, Windows Mobile, Windows, Mac OS Tiger/Leopard/Snow Leopard, Linux.
Google Gears Portable for FF 3.6
gears' source code
Learn how to perform GeoLocation with Google Gears