Automate and improve your web experience with Greasemonkey Scripts for Firefox
Greasemonkey is a free Firefox add-on that will let you install and manage user scripts to control the way you use the web. The Greasemonkey extension is useless without any scripts installed.
The first thing an eager user should do is find and install (or write!) a useful script. Scripts may be located anywhere on the internet or even offline. Installation of a script is most often done by clicking a link on a web page. One may also drag-and-drop a local file into the browser window, or optionally use the menu bar File → Open File… dialog to open it. Any file that ends in .user.js is a valid Greasemonkey user script.
When navigating to a user script, Greasemonkey will open its installation dialog instead of loading the script like a normal page. A thumbnail of this dialog is shown to the left. It displays the name and description of the script, if available, as well as the include and exclude rules that apply.
Among the numerous scripts you can install, there is an auto form filler, comment pre-fill for blogs, a Facebook tweaker, a google image ripper, a textarea backup, textarea resize, etc.