The coolest thing FF has over Chrome is the little [ev] icon next to an element that shows what events are connected to it. Saves me lots of time trying to track things down.

The coolest thing Chrome has over FF is that stepping through code is so much faster. There is no lag at all, while there is one in FF. It also has a "Search All" mode where it will look through all your code (html, js, css) to find a string.