Greasemonkey is a Firefox extension that enables users to download scripts that alter web pages to make them more accessable and useful. For example, you can download a script to add a “delete” button to Gmail, because it doesn’t have one. Or you can get rid of Google AdSense ads. Or get rid of the ads to the right of articles on CNN.com.

Right now, most of the available scripts add or remove elements from Web sites, but Greasemonkey has the potential to be much more powerful, actually altering the appearance of web pages and moving elements around. Once content leaves the provider and enters individual computers, people can manipulate it however they want.

nivi.com describes it well:

Greasemonkey lets you mash-up websites. It lets you extend and script websites and integrate that script right into the original site as if the designers had intended it to be there. It lets you use their web site, their data, their servers, their work to serve your purpose and function. There will soon be an army of hackers enhancing every site you use. Whether that site likes it or not.

While Greasemonkey may not be the future of the Internet, it’s a glimpse into the customization that users are going to be demanding. Companies are going to need to embrace increased functionality in order to keep users from simply taking content from the source and molding it to fit their own needs.

Download Greasemonkey

List of Greasemonkey Scripts

Greasemonkey screencast walk-through

nivi.com article