The difference is that unlike Brave and Vanadium, Firefox doesn't come with an ad blocker. You will have to install uBO. If you want to also trim tracking query params, you will have to enable a non-default filter list. Modifications like these will make you stand out from the average Firefox user. It's the reason why installing more extensions and messing with settings is not recommended when using Tor browser or Mullvad browser. The GrapheneOS project also discourages it (https://grapheneos.org/usage#web-browsing).

But you are still right, I don't have data for this or even a measure for uniqueness, it's just a guess.