Dragonfly is the development tool which comes with Opera
Chrome, WebKit and Safari Developer Tools
But I was surprised to see this very useful utility in it as well:
like I do, this is incredibly useful. The resource loading profiler additionally shows you how big all the files are your website are, and how long it needs to load them.
Internet Explorer Developer Tools
Since Internet Explorer is one of the slowest adapting major browsers out there, I rarely use its development tools, but it includes some surprisingly good utilities:
Why is FireFox not included here?
Simple: FireFox doesn't include development tools by default, you have to download them manually as addon. I'm using Firefox/Minefield, and unfortunately, there doesn't seem to be a working addon with the Minefield version I'm running when I wrote this, so Firefox has to be left out here.