Editors' Note: The Download Now link will prompt a local download of the Firefox extension. To install the extension directly, open the file using your Firefox browser.
The Professor X extension let's you see inside a page's head without viewing the sourcecode. Once installed the Professor X command is available by right-clicking as well as in the Tools menu. When applied to a page it will display the contents of the page's head element, including Meta, Script, and Style content.
Professor X can help you see how a Web site was constructed without having to go back and forth between the sourcecode and the page in your browser.