Greasemonkey - technical definition

A Firefox extension that adds programming functionality to JavaScript for creating more Web page retrieval options when using the Firefox browser. Greasemonkey "user scripts" can be used to eliminate pop-ups or certain parts of selected pages as well as extract information that is typically under the covers. Some scripts mix content from several sites.

A script can change the appearance of all pages retrieved or just alter the behavior of a specific page from one site. A myriad of scripts is readily available from the Greasemonkey repository. For more information, visit www.userscripts.org and www.greasespot.net. See Firefox.