FireFound is a Firefox add-on and companion Web service that I wrote for the Extend Firefox 3.5 competition in 2009. It allows users to track their device's location via Firefox's then-new geolocation API; additional features include the ability to view a device's location history on the website and the ability to turn on a "killswitch" that would clear your browsing data (history, saved passwords, etc.) if someone opened your browser and could not provide your chosen password. It was the first add-on of its kind, and it has been well-received.
That being said, FireFound will be shutting down on April 1, 2012. I don't have the time to keep it compatible with the newest Firefox and Firefox Mobile releases, nor can I keep up with the feature requests and bug reports.
FireFound users who would like to save a copy of their location data can, as always, export their data by logging in and clicking the "Download" button on the "My Data" page. Any users who have pre-paid for a Premium account past April 1 will be given a prorated refund.
For those looking for a suitable replacement, I recommend Prey. It's an open-source implementation of a similar idea, but it runs at the operating system level rather than inside the browser, so it's always on.
FireFound was shut down on April 1, 2012.