> The constant nonsense UI redesigns that come about with every new update. The instability, and ridiculous resources consumption. The slowness and slugishness.

I think this drives many people off Firefox. I am willing tinker with Firefox's internal CSS to tame some of the UI nonsense, but the rest of people just want a browser to get their work done; not to spend a couple hours every month to get rid of Firefox's new UI overhaul.