Greasemonkey is a Firefox extension that allows users to install scripts that make on-the-fly changes to most HTML-based web pages. As Greasemonkey scripts are persistent, the changes made to the web pages are executed every time the page is opened, making them effectively permanent for the user running the script.
Greasemonkey can be used for adding new functionality to web pages (for example, embedding price comparison in Amazon.com web pages), fixing rendering bugs, combining data from multiple webpages, and numerous other purposes.
