This is the software publisher's description.

You’ve arrived in a new city, a new continent, a new coffee shop. You don’t really know where you are, and are looking for a good place to eat. You pull out your laptop, fire up Firefox, and go to your favorite review site. It automatically deduces your location, and serves up some delicious suggestions a couple blocks away and plots directions there.

In order for this to be a possibility, your browser needs to know where you are.

Introducing Geode, an experimental add-on to explore geolocation in Firefox 3 ahead of the implementation of geolocation in a future product release. Geode provides an early implementation of the W3C Geolocation specification so that developers can begin experimenting with enabling location-aware experiences using Firefox 3 today, and users can tell us what they think of the experience it provides. It includes a single experimental geolocation service provider so that any computer with WiFi can get accurate positioning data.

The potential here is for more than just resturant lookups. For example, imagine an RSS reader that knows the difference between home and work and automatically changes it’s behavior appropriately. Or a news site whose local section is, in fact, actually local. Or Web site authentication that only allows you to login from certain physical locations, like your house.

Using Skyhook’s Loki technology to map the Wifi signals in your area to your location. Unlike normal GPS-based methods which can take upwards of 45 seconds for a lock, Geode works both inside and outside with an accuracy of between 10 to 20 meters, normally within a second.

Note that Geode is still in testing and is part of Mozilla Labs.