Color Scheme Designer 3
It allows you to alter everything to the nth degree in order to find a suitable scheme, and its interface will also teach you a bit about color theory in the process.
Goto Page
Adobe Culer It’s a Flash-based web application that allows you to browse color schemes from other users, edit color values to your liking, save them for others to find, and export as Adobe color swatch files. Its editor also includes a handy visual wheel to help understand the color schemes we discussed earlier.
Coluor Lovers Another great way to find new color combinations is to visit COLOURlovers, where a similar community-led approach is taken. http://www.colourlovers.com/palette/
Web Developer Addons
The Web Developer extension adds a menu and a toolbar to the browser with various web developer tools. It is designed for Firefox, Flock and Seamonkey, and will run on any platform that these browsers support including Windows, Mac OS X and Linux.
http://chrispederick.com/work/web-developer/
HTTPFox Addons
HttpFox monitors and analyzes all incoming and outgoing HTTP traffic between the browser and the web servers. Information available per request includes: - Request and response headers - Sent and received cookies - Querystring parameters - POST parameters - Response body
https://addons.mozilla.org/en-US/firefox/addon/6647
http://refresh-sf.com/yui/