Mozilla has cachet with nerds like us because of its history. Not because it's particularly better than alternatives or because it has enough of a user base to throw its weight around.
In contrast, they do test on Safari. They'd lose double-digit percentages of users if they didn't.
The ecosystem, unfortunately, generally has room for three top browsers. I'm not even sure Firefox is number four these days.
For obvious reasons, I don't think Google is devoting any resources to optimizing the experience of navigating to google.com for people who don't want any history generated on their use of google.com.
I agree with you that the other features listed are positives, but they don't appear to be positive enough to push use of Firefox psst Safari, Chrome, or Edge numbers.