The developer tools are pretty similar in my experience. I think it's maybe just that you're not used to it. And did you know that developer tools like this actually started in Firefox with the Firebug plugin?
Firefox is not slower with more complex web apps, you either have a (site) specific problem or are not judging fairly.
And even if you use Chromium, you are supporting Google's power position in browser technology influence. Which they use to push through web standard that benefit them, but not the users. Firefox has a more open ecosystem that is not focused on the benefit of one particular company.