I added Operator to my Firefox add-ons. Operator discovers microformat markup embedded in a web page: you can do some cool stuff, like extract contact information published as an hCard and export it to your address book, or you can discover what tags are used on a page, or you can add event information posted at Upcoming to your Google calendar.
I added this hCard to my Elsewhere page (and then punched it up to get the HTML to validate):
David Gorsline
nouveau@comcast.net
Reston, Virginia USA
And now, if you have Operator installed, you will see my info in the Contacts dropdown.
The expectation is that Firefox 3 will have microformats support built in.