Make this an href:

javascript:var windows={'mobile 240x320':[240, 320],'mobile 320x480':[320, 480],'small tablet': [480, 640],'tablet - portrait':[768, 1024],'tablet - landscape':[1024,768]},i,url=window.location.href;for(i in windows){if(windows.hasOwnProperty(i)){var params=windows[i],win=window.open(url,i,'width='+params[0]+',height='+params[1]);win.document.title=i;}}

It will open several windows at different sizes to test the responsiveness of your website.