Personally and strictly my own ignorant and informal opinion, Firefox and by extension Mozilla Corp. was doomed the moment it decided to compete with Chrome by being more like Chrome. Firefox built its userbase by being different than the dominant browser, then decided the only way to not die was to be exactly like the dominant browser except with less icky behind-the-scenes privacy behavior. That was a fundamental m…
I don't use FF because I still find SpiderMonkey (its JS engine) to be slower than V8.
As for which browser really is faster, it depends on the workload. Someone already linked to https://areWeFastYet.com/