Web Developer Firefox extension

This is an essential Firefox extension for website and blog owners. The plugin will add a toolbar to your Firefox, containing an extensive list of trivial and advanced features.Among other things the Web Developer extension will allow you to:

• disable cache, cookies, meta tags, redirectors, colors, etc.
• display image attributes, link details, access keys, forms, etc
• get information about the css, divs, anchors, block size, etc
• validate css, html, feed and links
• resize the window screen
• outline tables, frames, block elements, etc

You can download it for free here.