Though I hear Mullvad has its own Firefox fork now

Mullvad Browser? It's basically Tor Browser without the Tor, meant to be used with a VPN instead. It has integration with Mullvad VPN by default, but that add-on can be removed, and the browser doesn't need Mullvad VPN in order to function. Since the browser is based on Firefox, someone might want to fund Firefox development by using it with Mozilla VPN instead.