Citrix Receiver for Mac (11.6) allows to add only secure (https) stores.
If you are trying to add http store URL you may be getting this message – “Certificate Not Trusted – The Server might not be secure”.
So to add an http based store we need to generate the configuration URL from http://community.citrix.com/MacReceiverSetupUrlGenerator/
Enter Store Description, Store Address and Click Generate URL
Click on the Generated URL and this should launch and configure your Citrix Receiver with the specified store.
Click Continue and login into Store.