The plan was (is still, I think) to have Mullvad Browser “sunset” arkenfox once it is ready.
I haven’t seen it mentioned here before, but Mullvad Browser is currently working on “Persistent mode,” which will also remove the specific need to use Mullvad Browser for regular browsing and use arkenfox for login once it is shipped, and just using Mullvad Browser for both would be the recommendation.
But I guess that would be discussed in a new thread once it lands.