When a user clicks on the Mobile link at the bottom of a page, a cookie is set mf_useformat. This extension doesn't currently check for the presence of that cookie. I have created Phabricator task T373268 to deal with this, and have attached Patch 1065831 to the task to fix this. I have tested on an external wiki and the patch is working well.
Topic on Extension talk:MobileDetect
Merged, thanks!