It's the scratchpad script where you copy/paste into the about:config console. I just did it for the new v.115 release. I've done it previously but I don't have any set schedule. I guess 1x every six months (2x/year) seems sufficient but I wanted to see what others do.
Yeah, I do that too but every now and then I'll run the cleanup.js script. It always clears away a couple of deprecated prefs. I guess there is no harm in having those older prefs around but clearing them away seems nice.
You'll definitely want to run the prefsCleaner.sh script at the same time you're running the updater.sh script. The cleanup.js is more of a nice to do, than a need to do.
Ever since mullvad-browser came out and I saw the Arkenfox main developer basically endorsing it as the next logical evolution of Arkenfox.. I've only been using mullvad browser, no need to do updates.
Mullvad is great for people who don't want to tweak their browser settings very much. But lots of us see the tweaking as a feature, not a bug. I customize the heck out of my browser and appreciate that FF allows for the customization.