Yeah, as I said it was pretty lame how they added it in. I will repeat that I think it's still not as bad as how other mainstream browsers add unwanted features but I'm out of the loop there and could be wrong.
Strange, only once do I recall seeing a pop up from Firefox, which was letting me know another browser was trying to become my default browser which I did not do or want. So in that case it was useful, as it was Edge and I did not want Edge to be my default browser. That was years ago, back when I still used Windows. Not saying it doesn't happen of course, you have links I could check which I assume show it does, but I have not personally witnessed it happen in a long time.
I use Mull on my phone. Haven't gotten around to playing with Librewolf but it is on my list of things to do.
I don't consider the addition to be an anti-privacy feature however. I'd like to see someone change my mind about that.