Well, in js performance it is unfortunately behind in some benchmarks as far as I know. And some major non-standard website refuses to run under firefox, like teams unfortunately (definitely the fault of Microsoft)
So I am an FF user by ideology, but sometimes do use Chromium (basically only to not have to run electron).
Being "behind in some benchmarks" is not an argument at all. You're implying that
1. Those test convey any useful information leading to
2. The average user is able to notice the difference in the real world
I think that things that are not js execution time for actual site functionality are much worse for the overall web experience, namely js execution time for ads/trackers and overall latency caused by bad connection quality or bandwidth. The overall experience on firefox with ublock is en par with chrome with ublock for your average mom.
I am certain that I've used Teams in Firefox? I regularly use other 365 webapps as well with no problems (apart from troubles that are also present in every other browsers).
So I am an FF user by ideology, but sometimes do use Chromium (basically only to not have to run electron).