Just the fact that Firefox got browser tabs before anyone else, and Firebug, just took it to another level compared to all the other browsers available at the time.
Firefox was great because it was open source but it wasn’t ever really the “best” browser - it was the best open source browser.
Yes that was implied because IE was not mentioned either!
From https://fedoraproject.org/wiki/Firefox_Hardware_acceleration
I think that was around 2022-23.
I remember this affecting my laptop video watching a lot. Google meet feeling sluggish on Firefox is also something I remember until very recently..
They want to degrade the experience just enough to get you fed up with FF and go (back) to Chrome, without making it absolutely obvious that's what they're doing.
They often label these things as "regressions" because they don't test on Firefox and take forever to fix them. But I can't help but believe it's intentional.