A lot of the reason so many people seem to like Chrome Dev Tools better seems to be exactly the sort of "Works best in IE6" mentality that so many devs only spend time testing in Chrome and customizing Chrome Dev Tools how they like and making sure Chrome Dev Tools work right that it just becomes inertia that that is what they like better.
Little tweaks to sourcemap generation options, for instance, can be all it takes to get Firefox Dev Tools working just as well as Chrome for code debugging, but so many devs work in Chrome only that the defaults in so many places are accidentally so Chrome-centric.
Similar goes for all the Chrome-only Dev Tools extensions. At this point even the Dev Tools Extension Models are close enough between Chrome and Firefox that it mostly just needs more people using Firefox for development to catch up on extensions.