The Web Developer extension adds a menu and a toolbar to the browser with various web developer tools. It is designed for Firefox, Flock and Seamonkey, and will run on any platform that these browsers support including Windows, Mac OS X and Linux.
This would be your best CSS/XHTML helper I use it for debugging and testing and the best thing about it is that it’s portable and you can have it installed on any major browser and operating system. Check it out and instead of going back in forth in 4 different windows you can do it all in one.
