You know Firebug as a Firefox extension but there is also a "Lite" version which runs purely off JavaScript.

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Though all major browsers offer inspection tools you may like the Firebug style. Also, for me this is a lot better than the IE8 developer tools -- and it works in older versions of IE, too.

Get the bookmarklet over at http://getfirebug.com/firebuglite#Stable Show archive.org snapshot . It usually loads the JavaScript code from a remote server but you can also download it to have it run locally. If adding the bookmarklet does not work in IE, add a new bookmark manually and copy&paste the JavaScript link. Ignore the warning about "javascript:" being an unknown protocol.