It’s about the right list covering what Firefox has available right now for Web designers and developers:
http://www.instantshift.com/2009/01/25/26-essential-firefox-add-ons-for-web-designers/
Here’s a clip from the post:
It’s no secret that web designers and developers love Firefox! Firefox provides an endless amount of functionality that you simply won’t find in any other modern Internet browser.
One of the greatest aspects of Firefox is the ability to install add-ons to do just about anything and everything a browser can possibily do. As a web developer this functionality is extremely useful to us.
Firefox has some cool add-ons which make the job of website designers much easier. There are many useful add-ons for Firefox out there and we use several pretty much every day for work.