There are several ways to get mobile version in desktop browser:
1. The device=mobile parameter in URL (e.g. /index.php?device=mobile for homepage). The solution is to load /index.php?device=auto to switch to correct version.
2. The mjmarkup cookie with value of "mobile". The solution is to remove this cookie (load /index.php?device=auto should remove it too). Quite frequently it is happened if user opens website in Preview section and doesn't close it properly (via X button or clicking outside of preview popup). Also, in this case there is a related warning message displayed on MJ settings page.
3. Your browser is recognized as mobile (though it's very unlikely case). Try to open
www.mobilejoomla.com/uatest.php in your browser and check the value after "amdd" text, in the case of desktop browser it should be empty string ''.