FWIW, latest Firefox nightlies have caught up to Chrome in terms of performance. I have been a Firefox user since the 3.5 days, I was briefly swayed by Chrome because of performance until I came back for the Quantum update and stuck with it ever since. The updates have been great and Firefox + ubo + Nextdns is a solid combination.
Firefox has been and in some cases still is far, far worse than .2s slower, but even not considering that, the reality is that chrome has more support and thus gets more development and attention.
This results in some websites not working properly or at all on Firefox, while this isn't Firefox's fault it is a thing nevertheless
I'd be curious to know these sites because I've never had an issue with firefox loading sites, or even improperly. I do understand what you're saying though. I also stick with it because of the privacy "edge" (pun intended) over chrome+variants and I don't want a browser monopoly. Even though I'm just 1 person, it's something.
Nextdns has blocklists that you can configure something I could control. I used the free tier for a while, you get 300k queries a month which should be okay for personal use. The paid tier is $20/yr which isn't bad. I liked it so I continued to use it.