One or two devtool features are better in firefox, but when I gave it a good try a year or so back I had the devtools get stuck / crash / fail to find an element that's onscreen moderately often - enough that I'm not keen to use it for work by default.
Chrome is still significantly faster for me on multiple computers. Even now, Firefox can't smoothly scroll though this very page [1] without obvious jitter; no browser should have trouble with that.