greasemonkey is an add-on to firefox (extension) that
lets you to add bits of DHTML (“user scripts”) to any webpage to change it’s behavior. In much the same way that user CSS lets you take control of a webpage’s style, user scripts let you easily control any aspect of a webpage’s design or interaction.
It looks interesting… I’m just not sure I want to put it on my local copy of FF… maybe on my work copy….