I read an interesting article on hacks.mozilla.org the other day that I thought a few people may be interested in.
Its about a new DOM function, part of the Web Storage specification, that allows you to store data on a users local system.

Its written by Jeff Balogh, part of the Mozilla web development team
Link : http://hacks.mozilla.org/2009/06/localstorage/

hacks.mozilla.org is a site full of guides and demo’s of the new features that can be found in Firefox 3.5