Hi. Due to same policy origin you cannot invoke a link in JavaScript from foreign domain, which needs to be manually enabled on the backend, server side. Would you consider allowing requests from all domains?
Okay... This is weird, the same request from Chrome passes, and on Firefox it does not - due to error mentioned above. I guess this is Firefox additional "security method"... I'm surprised that it does not work on this single browser and works anywhere else 
If you can do anything from your side though... I'd be glad 
But I guess it may not be the issue with the BTT webserver