I would never trust the judgement of the most important piece of software on my computer to a small group of tinkerers maintaining a fork of someone else's massively complicated and deeply outdated source code. I don't care who they are—if they don't have a big enough reputation on the line, there's no reason to trust them.
I'm sure your cousin is super trustworthy, but that doesn't mean anyone should put him in charge of the armoured vehicles division of a bank.
Besides, it's a lot easier for a microscopically small and individualistic outfit like Pale Moon to never disappoint you compared to a large, managed entity like Mozilla which has disclosure policies and hundreds of employees each with their own priorities and agenda.
But for a limited use program like a browser, yeah, I want the people who won't disappoint me.
Also, my problems with the browser product itself are simple: the UI is awful and cannot be meaningfully fixed, and multi-process programs cause my computer to hang (so I set up a script to auto kill them). Pale Moon respects me as a User, not as an ad profile for Google.