The linked site uses AkamaiGHost, and the research shows that this service has a known issue when working alongside some proxies:
I guess that some server settings are somehow restricting the access when it comes from a proxied Win connection, but it doesn't look related to FIddler Everywhere as Fiddleris not changing the request in any way.
For some reason, on some requests I will always get a 403 response if Fiddler v5 or Fiddler Everywhere is running.
Here is a sample URL:
I'm using the default FiddlerScript.
Unfortunately, since the request only works without Fiddler running, I cannot capture the working request, so I'm unable to compare the two request to see what the difference is. I'm not sure how Fiddler is modifying the request.
I'm on Windows.