The shortest answer is: yes, it would be better privacy-wise to not change any of uBlock’s settings in Mullvad Browser. I can also give you a slightly longer overview:
To simplify this for you a bit, what it basically comes down to is:
- Increasing uBlock Origin protections (by e.g. enabling medium mode or adding new lists) will:
- Protect you from more naive trackers and mass surveillance, because your “attack surface” is reduced by virtue of running far fewer scripts.
- Keeping Mullvad Browser in its default state and not changing uBlock Origin settings will:
- Protect you from standing out from other Mullvad Browsers by more advanced (probably specifically targeted) trackers.
The key difference is that most trackers out there are not trying to differentiate between Mullvad Browser users in the first place, i.e. they are naive trackers looking to easily track as many people as possible, and not advanced trackers looking to differentiate you specifically from the crowd.
You have to understand your own threat model to determine whether this crowd-based protection is important to you.
If you are using both Librewolf and Mullvad Browser for different things, I would use these custom configurations like medium blocking mode in Librewolf to thwart naive trackers, and keep Mullvad Browser in its default state to better thwart more advanced trackers. Then you can choose between both as needed.
If you’re trying to switch to only using Mullvad Browser, whether you do this is up to you, but yes you are losing some of MB’s more advanced fingerprinting resistance properties by changing the browser’s behavior like this.