I have compiled a list of useful add-ons and tools to share with you all to make your life easier as a web developer:

FireFox:

Web Developer Toolbar - This is the swiss army knife and the all-in-one survival kit for web developers.
FireBug - This is a brilliant addon. It allows you to edit, debug and monitor CSS, HTML, and JavaScript live in any web page.[/url]
IE Tab - IE Tab gives you the option to see what your web page looks like in Internet Explorer.
Screengrab - Screengrab will give you the option to save an entire web page as an image.
Colorzilla - Advanced eye dropper, color picker, page zoomer and a few other useful tools.
Operaview - Operaview is an addon that allows you to see what your web page looks like in Opera.
XML Developer Toolbar - This is a very handy XML Developer's Toolbar.
Link Checker - Use this addon to check the validity of the links on any web page.
FireFTP - This will provide you with a built in FTP client in FireFox.
KGen Keyword Generator - Allows you to see what keywords are strong on visited web pages.
RankQuest SEO - You are only a few clicks away from carrying out most of your day to day SEO.


Internet Explorer:

Internet Explorer Developer Toolbar - This is a very useful developer toolbar for all you Internet Explorer users out there.

------
I have copied this from my website. Please do not re-post this anywhere.
-----