Userscripts.org maintains a database of Greasemonkey scripts, and for each it lists the URLs of web pages to which the scripts pertain.
Link: Userscripts.org
Geasemonkey is a Mozilla 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. Well-written Greasemonkey scripts can integrate changes so well that their additions appear to be natural parts of the web page.
Link: Mozilla
Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
Link: Mozilla
AgencyTool’s Web Design Dashboard is the definitive resource list for designing, developing, marketing & maintaining websites.
Link: AgencyTool