From the add-on's homepage:
Mouseless Browsing (MLB) is a Firefox-Extension which enables you to browse the internet with the keyboard. The basic principle is to add small boxes with unique ids behind every link and/or form element. You just have to type in the id and press enter (there is also an automatice mode available) to trigger the corresponding action i.e. following a link, pressing a button or selecting a textfield.
I could never get w3m working how I liked it so Mouseless Browsing really scratches an itch I have.