Preface

Greasemonkey is a Firefox extension that allows you to write scripts that alter the web pages you visit. You can use it to make a web site more readable or more usable. You can fix bugs that site owners can't be bothered to fix themselves. You can alter pages so they work better with assistive technologies that speak a web page out loud or convert it to Braille. You can even automatically retrieve data from other sites to make two sites more interconnected.

Greasemonkey by itself does none of these things. In fact, after you install it, you won't notice any change at all …until you start installing what are called user scripts. A user script is just a chunk of JavaScript, the same scripting language you use on your own web site. But user scripts don't run on your own web site; they can run on any web site, and they can do anything JavaScript can do. In fact, they can do more than that, because Greasemonkey provides special API functions that give user scripts even more power than traditional JavaScript.