You don’t want a randomised fingerprint, as that is relatively unique among a sea of fingerprints [1]. What you want is a fingerprint that’s as similar to everyone else (generic) as possible; that’s what Firefox’s resist fingerprinting setting aims to do, and what the Tor browser does.
[1] There are many values you can’t change, so the randomisation of the ones you can change could end up making you more unique … think of it like having your language set to french but are based in the USA — that language setting can’t uniquely identify the French in france, but will stick out like a sore thumb if set in shitsville Idaho. It’s likely the same if you use firefox but have your user agent set to chrome; that’s more rare and unique than not changing the user agent at all.