> You can also enable it on firefox with privacy.resistFingerprinting enabled.

Not the same thing.

I use both Firefox and Mulllvad Browser side-by-side on a regular basis and in practice Mullvad Browser is far more aggressive in its privacy preserving measures to the extent that you do sometimes stumble across websites that are "broken" in Mullvad Browser but work fine in Firefox, for example the animated map features on the Ventusky website (which, IIRC, breaks because Mullvad is more aggressive at blocking JS graphics functions).

FYI here are the listed differences between Firefox-/Tor-/Mullvad Browser: https://mullvad.net/en/browser/hard-facts