Sorry, Firebug
I used to tell people that I browsed the web with Chrome and developed with Firefox/Firebug. But it just occurred to me that I’ve completely abandoned Firebug when it comes to development and debugging.
The Chrome Dev Tools are just too awesome. A year or two ago they were still kind of clumsy for me, but they evolved rapidly and added a ton of features in a short period of time. I only expect it to keep getting better.