Cannot display my rails 4 app in iframe even if 'X-Frame-Options' is 'ALLOWALL'

I am trying to test a responsive design. I am using Rails 4. I know it sets 'X-Frame-Options' to SAME ORIGIN. So I overrided it in development.rb using

config.action_dispatch.default_headers = {
    'X-Frame-Options' => 'ALLOWALL'
  }

and it worked. I checked out the network request in the Chrome console and it is as follows:

But still websites like responsive.is and responsinator.com give me below error:

Refused to display 'http://localhost:3000/' in a frame because it set 'X-Frame-Options' to 'SAMEORIGIN'. about:blank:1

Whats going on??

Try just to delete this header 'X-Frame-Options'. Maybe this way in controller:

before_filter :allow_iframe_requests
...
def allow_iframe_requests
  response.headers.delete('X-Frame-Options')
end

I had the same problem as you, and searched for a solution to this problem all night.

I finally found out why it happens. It's because of the Chrome cache.

You can see the header['X-Frame-Options'] is ALLOWALL but it doesn't work.

Just try to open a "New Incognito Window" and go the same page and it works!

This problem only happened in development mode in my test. It worked fine in production mode.