I am not asserting that FF is bad and nobody should use it. I'm asserting that there are some people (at least one, anyway) who can't use it. Shaming people for not using FF is, therefore, uncalled for.
I just audited my system(firefox 110 on openbsd). and when dns is acting up(I disabled external dns leaving only my internal domains resolvable) firefox takes forever to do anything waiting on dns timeouts.
firefox is making requests to
www.google.com #why? I don't have google set as my default search engine.
detectportal.firefox.com
9.9.9.9.https #???? this is strange. DoH? but I should have it disabled.
contile.services.mozilla.com.
firefox.settings.services.mozilla.com.
content-signature-2.cdn.mozilla.net.
push.services.mozilla.com.
Well, Sigh, I have a new weekend project. poking around in about:config trying to turn this bullshit off off.
In any case, I really have spent a lot of time digging into this. At some point, I just had to let it go.
What machines, did you assemble the hardware yourself? On a reasonably modern android phone, firefox is fluent even with dozens of tabs and there's nothing you can do to make it slow.