Firefox has an extensibility plugin framework. This let’s you install scripts to control Firefox and the web pages you display. the coolest thing currently is Greasemonkey. This lets you intercept pages on a programatic basis and rewrite their html. You can make google display search links to Ask Jeeves… increase the size of text, hide images, block stories based on a regex, what ever you like.
Learn more here: Simon Willison’s Weblog
I’m listening to “Primer Amor” from the album “Stripped” by Aguilera, Christina