As of today, the W3C Geolocation API (widely associated with, though not technically part of, HTML 5) is support in the following major desktop browsers:
- Firefox (since 3.5)
- Safari (since 5.0)
- Google Chrome (version depends on OS)
- Opera (since 10.60)
- Internet Explorer (since IE 9)
There are at least two mobile browsers that implement the Geolocation API:
- Safari Mobile (since iPhone OS 3.0)
- Android (since at least Android 1.6)
On all of these platforms, you should be able to use navigator.geolocation.getCurrentPosition, etc.