This list is my personal choise for web developing, with 10 must have firefox extensions, below are ordered by preference.

Firefox extension for web developing

• Webdeveloper toolbar
• Firebug
• SEO toolbar
• Adsense notifier
• Firefox Accessibility Extension
• FireFTP
• Cooliris
• Screen grab
• Download helper
• Simple mail

Webdeveloper toolbar

This is a must have if you are a webmaster. With this simple tool you can test your website in diferent resolutions, see form code, edit CSS and see it in real time, and lots of other options that only this tool can provide.

Firebug

Provides you an easy way to debbug and edit any code on your website. It's also a powerfull tool if you are working with Javascript giving you a console for logging errors and watching values, with firebug you can measure time that your website need to load scripts and images.

SEO toolbar

This tool gives you precious information about yoiur website, between others this can tell you the PageRank, links to domain, page links, directory links, site age, monthly uniques, estimated traffic value.

Adsense Notifier

Display your earnings on Firefox bar, save time and see adsense money in real time.

Firefox Accessibility Extension

Acessibility toolbar lets you face the problems in your website, making a structured analisys, for someone with disabilities to view and navigate web content.

FireFTP

Simple easy to use FTP program.

Cooliris

Search for picture in google, yahoo, flickr, you tube, picasa and more. With a 3D full-screen this is a easy way to find what you are looking for.

Screengrab

It works like printscreen, but with this you can grab a selection or the entire page, to a file or to the clipboard.

Download Helper

Download content from you tube, meta café, dreamhost, porkit, daily motion with a simple click.

Simple Mail

Simple mail client for firefox.

You can grab the 10 must have firefox extensions, just search for it and install and is ready to use.