Eli Bendersky's website One of my heaviest uses of the mouse is browsing the Internet. Well, the burden can be greatly reduced by using the Quick Links feature of Firefox.
When on a webpage (but not typing in a text-box), click ' (that's the quote character, next to the Enter). Note that a small search toolbar, similar to 'Find' opens. Start typing the name of a link - Firefox will jump to it and you'll be able to navigate to the link by pressing Enter. This way it's possible to browse almost without touching the mouse at all!
P.S. Clicking / will open 'Quick Find', which is similar, but for all text and not only links
P.P.S. Check other shortcuts here.