Use Your Address Book in Firefox

Thanks to this, you can now import all your Gmail contacts to the local database and use this contact info to autocomplete forms anywhere on the web. You can also import data about your Twitter friends and if you are on a Mac, you can import your local address book as well. Contacts will also import avatars from Gravatar whenever they are available.

After installing the addon, you can test both the autocomplete and the tool's export features here.

Very cool idea. I can definitely the possibilities. I've Gone Google to Chrome, but I know I'll play with this sooner than later.