I checked it. I used the adblock.dns.mullvad.net
option and adblocking works fine on all browsers without using adblock extensions. The checker on Mullvad’s website shows the DNS info as it should.
I think maybe there’s no need for Firefox DNSoH settings anymore because the whole OS uses Mullvad DNS now. But I don’t know enough about DNS to be sure.
Voodoo Banshee