R. Johansson says it best. This is the single most important tool any web developer can have.
Web Developer Extension 1.0 for Firefox, Flock, and Mozilla has been released. There are many new features and bug fixes, so upgrading is highly recommended. The Web Developer Extension is a definite must have for any web professional, so if for some reason you don't already have it, download it now.
For more info and comments, visit Chris Pederick's blog post Web Developer 1.0.