If you're on Android, FF supports add-ons.
If you're on an iPhone, uBlock is now supported: https://apps.apple.com/us/app/ublock-origin-lite/id674534269...
There's also Orion browser, but I found it to be a bit more glitchy, especially around sites like YouTube (fuck the app, I'm not watching videos there): https://orionbrowser.com/
The uBlock Origin lite that can run on iOS is very limited compared to the uBlock Origin that runs on Firefox Android.
It's not the same thing at all. Mullvad DNS blocks all ads across the system.
Yes, I use Firefox on Android with ublock origin, it works great. But using adblocking DNS on your phone will also block most in-app ads which is a big quality of life improvement.
I could also use a VPN to keep my phone always on my home network and thus behind my own ad blocking DNS but Mullvad's adblocking DNS was really nice and convenient.