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

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

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Read more Show archive.org snapshot

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.