Everybody loves Firefox. Even if I use Safari as my main browser most of the time, Firefox’s expandability is still irreplaceable. With so many available themes, plugins and extensions, you can personalize your browser according to your browsing or work behavior.
So, what’s my favorite? Since switching to Mac, I do not test out everything one-by-one anymore but I have to say Chris Pederick’s Web Developer extension is one of the best of productivity purpose. It provides you with almost every tool you need as a web developer like customize how the CSS should be displayed, window resize, display outlines (tables, links, frames) and so much more.
For me this is perticularly important and makes everything easier to learn how a site or webpage is built.
This extension is available for Firefox, Flock and Seamonkey, and will run on Windows, Mac OS X and Linux.