The Professor X extension for Firefox let’s you see inside a page’s head without viewing the sourcecode.

One 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. This can help you see how a website was constructed without having to go back and forth between the source code and the page in your browser.

This is the companion extension to X-Ray although either can be installed and used on their own. They were created to help people learning web design at various levels of experience.

Get Professor X 0.4.1 from from addons.mozilla.org