Omg no. That is "Mullvad Browser" which is a version of Torbrowser with a preinstalled extension and no Tor. Basically an ad project for MullvadVPN, because Librewolf already exists.
Mull is Firefox Mobile + Arkenfox user.js, made by DivestOS developers.
Yes for sure, Mullvad Browser is fine. It is Torbrowser without Tor, I think that makes no sense so I would just use Librewolf with Mullvad VPN systemwide