I know that most browsers have discontinued support for being able to customize the onbeforeunload message however I came across this message on the Google DoubleClick website. Is this because it's a google website and they can do whatever they want?

something as basic as

window.onbeforeunload = function () {return 'Custom message'} 

to using https://github.com/codedance/jquery.AreYouSure . I'm going to assume that because the custom message I see in the image above is on a ddm.google.com (google advertising platform) that they can override their own rules?

edited because How can I override the OnBeforeUnload dialog and replace it with my own? is no longer valid due to changes in chrome and other browsers