Temporary fixing "This content cannot be displayed in a frame" in Office365 with Internet Explorer

When I was branding an Office365 SharePoint 2013 site, I'm getting an error when viewing apps that use Web Parts.
The error message is "This content cannot be displayed in a frame" and is described similarly to this forum thread.

https://social.msdn.microsoft.com/Forums/en-US/appsforsharepoint/thread/fa6abb31-7251-4744-ab14-634cde38a42d

The "temporary fix", is to add “https://login.microsoftonline.com” to the Trusted Sites list in Internet Explorer.