Greasemonkey is a Firefox extension that allows you to write scripts that alter the web pages you visit. Dive Into Greasemonkey is a popular free book about programming with Greasemonkey.
Get latest version of Greasemonkey and ensure it compatible with your Firefox version. Dive Into Greasemonkey is a free download, available in a variety of formats. If you dont wish to download it, Read it online for free.
It has chapters on Getting Started with installing greasemonkey, installing and managing user scripts, creating greasemonkey userscripts, debugging user scripts, studying Common Patterns, and explanations with relevant Case Studies.
How was this book developed – Mark Pilgrim, the website owner says
“Dive Into Greasemonkey grew out of discussions on the Greasemonkey mailing list, and out of my own experience in writing user scripts. After only a week on the list, I was already seeing questions from new users that had already been answered. With only a few user scripts under my belt, I was already seeing common patterns, chunks of reusable code that solved specific problems that cropped up again and again. I set out to document the most useful patterns, explain my own coding decisions, and learn as much as I could in the process.”
Greasemonkey is a powerful tool that can significantly alter the web pages you visit. Userscripts.org also has a more complete list of GM userscripts.