I installed Chrome because its fast. I liked it for web development because it had "Firebug" essentially built in. I eventually peeked back at Firefox to see if was doing anything interesting on the development side, but by that point much preferred the overall speed and simplicity of Chrome that I simply haven't bothered to go back.
Compared to IE, developing for both platforms rarely requires you to even check Firefox for correctness or performance once you get around the quirks or use more recently developed JS libraries.
I think the only extension I installed for Chrome was TamperMonkey. And a couple of things developed for work purposes.
And people here have told me that I'd like the Chrome dev tools better, but although I tried I was too lazy to completely switch so I just use FF and Firebug.