2 solutions
ou
function openUrl( url='https://www.youtube.com/watch?v=uWH00ehhLP8&list=RDCLAK5uy_mCvOm3kQy1RTBwDOGYkNhtHwMO89ffquk' ){
// https://stackoverflow.com/questions/10744760/google-apps-script-to-open-a-url
var html = HtmlService.createHtmlOutput('<html><script>'
+'window.close = function(){window.setTimeout(function(){google.script.host.close()},9)};'
+'var a = document.createElement("a"); a.href="'+url+'"; a.target="_blank";'
+'if(document.createEvent){'
+' var event=document.createEvent("MouseEvents");'
+' if(navigator.userAgent.toLowerCase().indexOf("firefox")>-1){window.document.body.append(a)}'
+' event.initEvent("click",true,true); a.dispatchEvent(event);'
+'}else{ a.click() }'
+'close();'
+'</script>'
// Offer URL as clickable link in case above code fails.
+'<body style="word-break:break-word;font-family:sans-serif;">Failed to open automatically. <a href="'+url+'" target="_blank" onclick="window.close()">Click here to proceed</a>.</body>'
+'<script>google.script.host.setHeight(40);google.script.host.setWidth(410)</script>'
+'</html>')
.setWidth( 90 ).setHeight( 1 );
SpreadsheetApp.getUi().showModalDialog( html, "Opening ..." );
}