CSS Usage : CSS Coverage is an extension for Firebug which allows you to scan
multiple pages of your site to see which CSS rules are actually used in your site.
Firebug : You can edit, debug, and monitor CSS, HTML,
and JavaScript live in any web page.
Greasemonkey : Allows you to customize the way a web page displays or behaves, by using small bits of JavaScript.
Hundreds of scripts, for a wide variety of popular sites, are already available at http://userscripts.org.
You can write your own scripts, too. Check out http://wiki.greasespot.net/ to get started.
User Agent Switcher :
The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
View Source Chart : Source Charting...* Defines HTML Tag Boundaries (so you don't have to)
* Defines DOM Structure and Hierarchy (so you don't have to)
Web Developer :
The Web Developer extension adds various web developer tools to a browser.
YSlow : YSlow analyzes web pages and why they're slow based on Yahoo!'s rules for high performance web sites.Posted by 홍반장