Add jquery menu plugin for mobiles/tablets to our prestashop site

To adapt this flexnav jquery plugin (here is the link: [login to view URL]) on our website when displaying on mobiles or tablets only. Our site is based on prestashop cms and it has a kind of complex css (8000 lines and it got different responsive functions). You will be very careful not to harm the normal styling and functions on the desktop version and keep what it is already done on the mobile/tablet site version, except the menu system (off course)