When it comes to Firefox, these are my top 5 favorite extensions that aid in development:
ColorZilla – An advanced eyedropper, color picker, and page zoomer
Html Validator – Adds HTML validation to the View Page Source window.
Split Browser – Splits the browser window so that you can view multiple pages at once.
Web Developer – Adds a menu and toolbar that’s packed with web development tools.
YSlow – Helps determine how a page is performing.
why isnt firebug in the list?
I’ve used Firebug in the past and it is actually really powerful. It’s strange, I have it, but I actually don’t use it that often. Usually the Error Console gives me enough clarity to know what script/CSS issues I have. I probably should make Firebug part of my arsenal. I’ll start toying with it more and perhaps it just might make it onto the list. Thanks for the tip!