Last time I did a DOM benchmark Chrome still beat it by a significant margin. Also, only personal experience, but Chrome seems way more responsive with multiple tabs open than Firefox.

One annoying thing is that current versions of Firefox seem to rely on disk I/O too much, so if it's busy, you can't really do anything (switching or creating new tabs is greeted by spinning loading circle that takes a long time to happen).

On the Mac, Safari is far more power efficient. With each update I notice Firefox is using more and more ram too. Also good luck finding out which tab is causing problems.

IIRC, the complaints I've read online are along the lines of: Mozilla ran a Mr Robot ad campaign with browser integration, partnered with an ad company for some research in a seemingly-sneaky way, made their CEO resign (now the CEO of Brave) because he donated personal money to an anti-gay marriage lobby effort, forced pocket integration for ad revenue purposes, and they deprecated their extension api which broke most extensions that did not get updated.

I'm not saying anything in favour of or against these decisions, they're just what I remember reading people complain about over the last year.

edit: typo and clarification