I generally like Chrome dev tools better, but Firefox (and Firebug, RIP) has some unique tricks, in practice I use both at times. But I agree a lot of people take your approach of Chrome as default, Firefox/other for testing, and that's part of the problem. (If you haven't heard of Selenium+SauceLabs, they can help with your automated testing of multiple browsers.)

I still use Firefox as default, both for developing and for general web browsing. It and my set of extensions fit my preferences too nicely and have no equivalent in Chrome. I use Chrome at work primarily for Google Hangouts / Meet, the occasional debug session, or just to have another session. (Trying to get into Chrome's Profiles feature too.) At home I just use Chromium from time to time, mostly because my computer is starting to age and I notice the performance difference for certain things.