The Web Developer Extension adds a menu and a toolbar to the browser with various web developer tools. It is designed for Mozilla Firefox and Mozilla, and will run on any platform that these browsers support including Windows, Mac OS X and Linux. The extension is highly configurable and contains many powerful features including CSS manipulation, multiple validation options and tools to display information about the current page.
Pros: The Web Developer Extension is easy to install and has tons of useful web developer tools, such as live CSS editing. The Web Developer Extension is a cross-platform Firefox extension for Mac, Windows, and Linux.
Cons: None significant.