Um. Have you tried this? Because obviously based on my comment I've done this before (and I've of course included Firefox).
I just did this again and sites tell me Brave has a randomized fingerprint. Firefox's is "unique". A specific example: the EFF Cover Your Tracks website[1] said that both browsers convey 18.21 bits of identifying information.
Additionally, if you need to enable a certain setting for best performance, that browser is obviously worse for purpose, given that the vast majority of people don't change settings.