I was going to switch to Waterfox in light of this news, but a cursory search revealed that it, too, was sold to an advertising company not long ago. While they have published a blog post opposing Mozilla's AI stance, I'm really past the point of giving ad companies any benefit of the doubt.
I'm looking into Librewolf now.
Your cursory search likely provided outdated info. [0] Quoting from it's maintainer: [1]
Waterfox is independent again: [0]
And System1 are an “ad-tech” company but the term should be used loosely. The ownership made sense as they are a search engine aggregator and they own a bunch of old school search engines like DogPile, InfoSpace etc. Nothing to do with what people associate ad-tech with, i.e. tracking you across the web or collecting personal data.
The browser situation grows more grim by the day.