FFOS was doomed because the pixel explosion wasn't just stretching the GPUs of that time, it had also made CPU rendering a serious bottleneck, a fact the Android team also struggled to accept. Mozilla lacked the resources to do anything about it, although I didn't get the impression they actually understood the problem at all (as shown by it not being mentioned here), while the Googlers resorted to that most Googly of activities: arguing via walls of text that try to deny the obvious truth.
I have long maintained that what Mozilla should have done was a Firefox OS based e-reader. The mania that exists for all things e-ink in the tech industry is real, and if you combined that with a proper open platform you could leverage it into being a self sustaining business.