This problem should no longer exist for developers using Microsoft Edge. If you experience issues with localhost testing, navigate to about:flags, and make sure Allow localhost loopback is checked.
Microsoft Edge does not currently support (out of the box) localhost testing. You can however enable it by following the guidance provided here: http://dev.modern.ie/platform/faq/how-can-i-debug-localhost/.
We’re working on resolving this in a future release.