Firefox has been doing a few rather questionable things. They had the Mr Roboto add-on which was pushed out to advertise a TV show, they stuck ads in the "Recommendations" [1], they proactively destroyed peoples' bookmarks when they dropped support for RSS, they dropped support for RSS (because, apparently, a decentralized way to track website updates is anti-Google), and they destroyed a lot of useful add-ons.
Waterfox is good if you miss the old add-ons from pre-quantum Firefox. But it is the old model, and one lagging page will still hose the whole browser.
I tolerate it because I need my Downloadthemall extension, amongst others.
I basically can't trust them anymore.
[1] https://www.theverge.com/2018/5/7/17326184/firefox-ads-spons...