Why Developing for Firefox is Torturous

This is an interesting take that I hadn't really heard before.

I find the complaint about the JS engine being slow interesting. I was under the impression that Mozilla had largely closed the gap, but performance differences still existed (but possibly not all in Google's favor). I wonder if he's developing on Chrome, and thus implicitly optimizing for it, and noticing the problem areas where the engines don't have matching characteristics? Then again, maybe Mozilla still has some JS engine areas that really need improvement.