Opt Out not working in IE 11


we included the opt-out iframe in our portal:
<iframe style="border: 0; height: 200px; width: 600px;" src="https://<CUSTOM_URL>.com/index.php?module=CoreAdminHome&action=optOut&idsite=1&language=de"></iframe>

The iFrame is showing up in our portal and it works.
BUT! When you try to disable the traking and you click on the checkbox to disable, then in IE 11 opens a new Tab. In this Tab is open a dialog with: “The displayed web page tries to close the tab. Do you want to close the tab?” Here you can select yes and no.
No matter what you click, nothing happens. The newly opened tab simply stays white and when you change back the checkbox of the opt-out iframe is still set. You cannot deactivated it.
In Firefox and Chrome all works fine.

The DevToolbar in IE shows an error:
The “closed” property of an undefined or null reference can not be retrieved.
In index.php, row: 16, column: 17

The problem is may the close function here:
if (newWindow.closed) {

Now, we need help :slight_smile: