Vimperator is a firefox add-on that enables a VIM like experience. For the most part you can say good-bye to the mouse.
http://vimperator.org/trac/wiki/Vimperator
I am still getting use to it but I really like the ability to navigate without having to move my hand to the mouse.
Ubiquity is yet another firefox add-on that brings web services to you. Say for instance you come across a word that you don’t know. You could simply select it and then then with ubiquity type ‘define this’ and you’ll get the definition.
Mapping and other functions work similarly…
https://wiki.mozilla.org/Labs/Ubiquity
One thing to note is that there are still some problems and certain functions still don’t work correctly.