I wonder how many of the people who say "Firefox is significantly slower than chrome" are using windows... On my computer, Firefox IS slower than chrome but (with ad blockers enabled) by an insignificant amount. By still being "the last remaining mostly independent, maintained and reasonably popular browser" I'd prefer it to use over chrome even if it is a bit slower.
Of course, ms is no longer the "old micro$oft" but their history on how they handle competitor browsers makes one think how much interest they could have in investigating and fixing such a bug.
My takeaway is: prefer independent software as much as you can.
I have heard the most complaints from Mac and Linux users on HN and Reddit. Especially with Youtube...
Windows + Firefox is just fine in my experience. After the Quantum upgrade/version. Yes Chromium based Edge and Chrome is a bit faster, Opera and Vivaldi feel slower depending on the number of tabs.
Firefox and Edge handles many tabs the best from a performance perspective on Windows in my experience. Vivaldi is very close.
Anything without vertical tabs is impossible to use with many tabs.