My Chromium-using coworker is jealous of my (Firefox's) 3D View and my Responsive Design View. I use both browsers in order to have access to all the best tools.

(I keep development separate from regular browsing, either through Incognito or separate Firefox profiles. This way, my regular browser addons don't distort my view of how-my-website-looks-to-most-people, and Firebug speed becomes irrelevant.)