I actually tested this and Firefox is significantly faster in rendering CSS and tables. (Not sure about complex Javascript.)
Chrome's snappiness is mostly UI smoke and mirrors, actual sites load faster for me in Firefox.
I'm still not a fan of the latest UI revision on Firefox.. Chrome is able to make me forget there is an UI
I remember switching to Chrome because of a new UI update many years ago (performance too)
If Firefox manage to catch up performance wise, I might give it another try