I haven't done much front-end development of late but I recall the days for front-end web devs where if you weren't doing it in Firebug you were doing it wrong. Then Chrome Dev Tools changed everything... have the Firefox Dev Tools caught up with Chrome Dev Tools yet?
Firefox has been providing amazing developer tools for a long time already. In some areas they are better than Chrome's, and vice versa. Just give it a try and see for yourself.