it's open source, you can simply look at the code (or, better, at the differences with firefox)
I have LibreWolf installed and I use it from time to time (although I prefer Brave), but I don't have that much trust in project as is. I think if it had sponsorship and could afford to pay a few reputable pro-privacy developers to maintain the project then there's less risk, but as it stands is anyone honestly looking through all the source code to validate their pro-privacy claims? And even if they did, could you trust them or their releases?
Are you really serious? Firefox source is 21 million lines of code.