Mozilla took away perfectly good functionality and gave existing fans a big middle finger while doing so. Although I am a fan of Mozilla, it is entirely understandable to me why someone wouldn't want to keep using their products.

And lets not ignore the fact that most sites are designed with Chrome as their intended target. FF simply doesn't work as well on many sites.

What's difficult to understand? I've been using Firefox as my main browser because of the extensions while choosing to miss out on features that other browsers had and Firefox didn't. Simply because the pros outweighed the cons.

I still use it as my main browser at home, but with the extensions that used to set Firefox apart gone and forced to reset my workflow and expectations to the minimum common functionality, I find myself using Safari more and more at work simply because the battery usage is better and has out of the box support for SPNEGO. As an added bonus, I can watch HD videos smoothly without killing my processor and draining my battery.

Not really. I gave up Firefox (as my main browser; I'm a web dev so use all of the major ones regularly anyway) because the main thing keeping me there was its extensibility, and that advantage went away. Firefox was and remains slower, less reliable, and less capable than Chrome, and IME has actually become worse in those respects as well since Quantum.