If you are a web developer and you use Firefox for your browsing/testing/debugging/CSS needs you HAVE to get these tools:

Web Developer Extension and Firebug

Anytime I’m on anyone else’s computer now I miss these tools dearly. You really get spoiled. Oh and did I mention they’re completely FREE?

Web developer extensions lets you edit both CSS and HTML in real time so you can tweak things live on a page. It also comes with a million other really useful features like a ruler, validation, speed test, ability to see and dissect every type of element – forms, images, divs, etc, etc. Way too much to get into here, but I’ll say this: spend a few hours exploring all the options and you’ll be amazed at how much it lets you do – it will really cut your development/debugging time in half.

Firebug is sort of similar in that a lot of the features overlap. I hear it’s very popular with javascript coders. My favorite feature is the live inspect tool that gives you instant information about elements as you mouseover them.

Instead of trying to go over all the features, just check them out for yourself:

Web Developer Extension and Firebug