How these two compare to Dragonfly[1] (Opera). I never worked in depth with any of them so they look pretty same to me. Only difference I know is probably remote debugging which Opera had for years but there was no need for it in firebug/chrome dev so I wouldn't count it as an extra feature.

1. http://www.opera.com/dragonfly/features/ / https://bitbucket.org/scope/dragonfly-stp-1