Google Apps Script HtmlService favicon gives mixed insecure content warning in Safari

GAS HtmlService now allows us to set a favicon for our web-app as explained here :https://code.google.com/p/google-apps-script-issues/issues/detail?id=2005

However, this will works flawlessly only in Chrome. In Firefox and Safari, I get the following error: Loading mixed (insecure) display content "http://www.google.com/url?q=<favicon url>" on a secure page

Safari refuses to show the favicon, where Firefox still shows it (don't care about IE). Now, the favicon I used is specified with 'https' and is accessible over https (hosted on imgur).

var html = HtmlService.createTemplateFromFile('page')
      .evaluate()
      .setSandboxMode(HtmlService.SandboxMode.IFRAME)
      .addMetaTag('viewport', 'width=device-width, initial-scale=1, maximum-scale=2.0, user-scalable=yes')
      //.setWidth(400)
      //.setHeight(300)
      .setTitle('...')
      .setFaviconUrl('https://i.imgur.com/<filename>');

Does anyone know how to make the favicon load using https correctly to avoid getting the warning and have it load in Safari as well?

Solution

This looks to be a bug; it has been reported to the Google team.