Thread:Project:Support desk/mobiledetect theme works on the login page but changes back to standard after login/reply

Extension:MobileDetect? The extension conditionally sets. Once a user registers, the value of $wgDefaultSkin is copied to their preferences. From that point forward, the skin set in their preferences will be used instead of $wgDefaultSkin. If you want this to be used for registered users too, you'd need to conditionally modify user preferences as well.