Why does only IE check the X-Frame-Options Header when iFrame src sends a file?

Question

Debugging a strange problem, I stumbled across an interesting behaviour:

On a web page, I trigger a file download with the following JavaScript code:

var iframe = document.createElement("iframe");
iframe.src = 'download.php';
document.body.appendChild(iframe);

The PHP script download.php sends a text file with the X-Frame-Options header set to DENY:

<?php 
   header('X-Frame-Options: DENY');
   header('Content-type: text/plain');
   header('Content-Disposition: attachment; filename="text.txt"');
?>
Text

Chrome and Firefox allow the file download, IE 11 shows an iframe with a message saying the content can't be embedded.

What is the correct behaviour? To me, it makes much more sense what IE does.

Answer 1

X-Frame-Options exists to prevent click-jacking. Preventing a file from being downloaded is not something that X-Frame-Options aims to achieve, since such a restriction can easily be bypassed by opening a link in a new window.

Therefore the behavior of Chrome and Firefox is correct.

_{(See also https://crbug.com/331211 "The X-Frame-Options flags aren't intended to prevent downloading. They only prevent displaying the page as a subframe.")}