Firefox has significantly improved and deserves praise for it. Rewriting history to always be at war with Eastchromea is unnecessary.
I agree that when a tab would crash FF would die in spectacular ways but this was perhaps a once a month experience? Tab restore brought everything back each time. As a result I usually only opened Chrome for site testing.
I've been om FF the while time and I'm impatient.
In the other hand I've no reason not to believe it when so many people report performance issues.
My best guess is a combination of different browsing habits and/or different hardware/os.
(My browsing habits are mostly hn, local news and pages I work on and I've had decent hardware running various versions of Linux and Windows.)
1: At first I didn't know how to get sites to default to a container, so kept having to close and reopen tabs to get the right contianer, but once I figured that out, it's smooth.
The benchmarks have always been respectable. I'm sure there are some configurations that made it work poorly, and that's a problem. That isn't true in general.
I too found Firefox pre-57 slow and switched to Chrome. That was because the user experience was slow, slow to open, slow in UI responsiveness, slow to make websites actually usable. Everything had this UI lag feel.
I'm sure it benchmarked fine, but I am a human, not a JavaScript benchmark.
I don't know how to tell the difference between "Firefox is slow" and "Firefox has an undeserved reputation for being slow."
I just installed Chrome besides Firefox back in the days and it was much snappier. This became my new baseline.