3 must have developer tools for Firefox

There are some developer tools which I can't live without when developing using Firefox. They have saved me countless hours and simplify the entire development experience, here is a list of my top three recommended Firefox add-ons.

Firebug
This firefox extension is by far the single most useful tool when developing a website, it has the ability to modify HTML or even CSS live on the website. This means that you don't need to go and make changes to the actual code and refresh only to find it's still not working - you can adjust the code right through the open browser window and the changes will be updated automatically.
Download here

Web developer toolbar.
While Firebug does cover a significant portion of this toolbars functionality, it still does have a lot to offer such and ability to manage your session cookies, images, JavaScript and advanced form handling functionality.
Download here

HTML Validator for Firefox
One of the most frustrating things I find about using the online validator is that it can only validate public facing URL's. Meaning that if you're developing on your local server or a page behind .htaccess authentication there's no way for you to check if the page is valid HTML mark up. Well with this nifty tool you'll be able to validate any page without an internet connection, meaning that you can validate any web page directly through your firefox browser.
Download here