I primarily use Firefox for browsing, but for development I usually use a mix of Firefox and Chrome. It might be just me, but it's very common when I use the JavaScript debugger in Firefox that it either freezes the site, the debugger, or Firefox itself. That causes me to give up and head to Chrome. I also wish they put a visual queue on the web page when you pause the debugger like Chrome does. Everytime the site get's unresponsive I have to click around few times, wonder what I screwed up, and then realize that the debugger was paused.