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.
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on my computer to a small group of tinkerers maintaining a fork of someone else's massively complicated and deeply outdated source code.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.
Mozilla is morally wise a totally unacceptable developer. They have been on the good side in the past, but what is left is almost as disgusting as Google itself... the Google - which Mozilla tries so hard to become itself.
— How quickly will serious vulnerabilities be patched?
Given the project is so small, I wouldn't trust their future response to be rapid even if they have been in the past. Right now most security fixes come in the form of merging upstream security fixes from Mozilla. As their code base becomes increasingly divergent to the Firefox head, merging in upstream security fixes will become increasingly difficult and increasingly cumbersome.
— How much do you really trust these developers?
I don't think many people realise just how important your browser is when it comes to trust. When you access online banking, your browser is in ultimate control of the entire trust chain. Your browser validates the security certificates. Your browser decides what to do with the passwords you enter. Your browser decides what to show you in the address bar.
— What's wrong with Firefox 67+ anyway?
The one thing everyone seems to cite when they say they use Pale Moon or Waterfox is that they still support the older extension system. The reality is all important extensions were unaffected. And while some genuinely useful extensions were lost in the transition (e.g. DownThemAll) most should be standalone applications anyway.