If you want to make Minerva the default skin for desktop devices, the obvious way would be to set `$wgDefaultSkin = 'minerva';` in your LocalSettings.php, right? It works, but when you vist the Special:Preferences you get a fatal "MWException from line 151 of includes/Preferences.php: Global default 'minerva' is invalid for field skin". I checked `$wgValidSkinNames` and Minerva was included, I checked `$wgSkipSkins` and Minerva wasn't there.
So I tried forcing the mobile view using `MobileContext::singleton()->setForceMobileView( true );` as instructed in the extension documentation, but the MobileContext class wasn't found (the documentation should be somehow updated). Then I tweaked the `$forceMobileView` property directly at the source code of MobileFrontend and Minerva showed up, but the link to the preferences section was no longer there. Instead I got the mobile settings section, which wasn't what I was looking for.
In the end I came up with the following hack. By setting `$_GET['useskin'] = 'minerva';` directly in my LocalSettings.php, Minerva shows as the default desktop skin. It isn't perfect, but it's good enough for my use case.
I think that it should be possible to set the Minerva skin as the default skin for desktop devices. All it would take, I think, is to fix the fatal exception I mentioned earlier.
I'm using MediaWiki 1.27.0 and the corresponding MobileFrontend branch.