Tools like Firebug for Firefox, WebKit’s Web Inspector and Opera’s Dragonfly are indispensible tools for front-end Web developers, letting you view the DOM as the browser sees it.
And that’s where these tools can actually cause some problems, or at least a bit of confusion. When you choose “Inspect element� or otherwise bring up one your browser’s DOM inspector, what you’re looking at is the document tree after the browser has applied its error correction and after any JavaScripts have manipulated the DOM. It is not necessarily the same as what you see when you choose “View source�.