XML Element not found Problem

I have IIS 8.5 (Windows 8.1) and a WCF application that I have setup (from VS2013 Express) to be published onhttps://localhost/myserv/thisisit.svc When testing it with Firefox I get error "XML Parsing Error: element not found location:https://localhost/myserv/thisisit.svc", when with IE it gives off error HTTP 400, when with Chrome it gives a blank page.

However, when testing EXACTLY THE SAME URL WITHOUT HTPPS (I mean: http://localhost/myserv/thisisit.svc) it runs perfectly saying "ThisIsIt Service You have created a service. To check this service, you need to create...". Why is this error happening and how can I correct it?

Note that when I connect to the service and execute some code of a function by a self-made executable (VB.NET, VS2013) it returns the CORRECT value, even with https...