greasemonkey: Take Back the Web, Really! – greasemonkey: index
Greasemonkey is a Firefox extension which lets you to add bits of DHTML (“user scripts”) to any web page to change its behavior. In much the same way that user CSS lets you take control of a web page’s style, user scripts let you easily control any aspect of a web page’s design or interaction.

So, here it is, a little javascript here, a little DHTML there and, ta-da, you get control over those annoying webpages made useless by clueless webmonkeys:) That’s right, strip out the ads, point ot print versions, suppress navigation areas, all the power goes back to you.