responsive layout preview in the media tab needs config setting up, this is the default:
"cms-responsive"=>array( "desktop"=> array("w"=>"100%", "h"=>"500px", 'img'=>'/images/wildfire/icons/responsive/desktop.png'), "phone_portrait"=> array('w'=>'300px', 'h'=>'352px', 'img'=>'/images/wildfire/icons/responsive/phone-portrait.png'), "phone_landscape"=> array('w'=>'468px', 'h'=>'202px', 'img'=>'/images/wildfire/icons/responsive/phone-landscape.png'), "tablet_portrait"=> array('w'=>'750px', 'h'=>'920px', 'img'=>'/images/wildfire/icons/responsive/tablet-portrait.png'), "tablet_landscape"=> array('w'=>'1010px', 'h'=>'660px', 'img'=>'/images/wildfire/icons/responsive/tablet-landscape.png') )