When using Google Chrome to access any site hosted on IIS 10.0, the error ERR_SPDY_INADEQUATE_TRANSPORT_SECURITY is encountered. When using Mozilla Firefox to access any site hosted on IIS 10.0, the NS_ERROR_NET_INADEQUATE_SECURITY error is encountered.
The same sites function as expected in Internet Explorer and Microsoft Edge.
By default, IIS 10.0 (which is installed on Windows 2016 by default) has HTTP/2 enabled. This is not supported in the current default configuration of Google Chrome and Mozilla Firefox.
For more information, please see this Microsoft resource.
This can be addressed on the server-side by setting the following registry keys and the restarting the host Windows server:HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
EnableHttp2Cleartext DWORD (32-bit) Value 0
This can be addressed on the client-side by enabling support for HTTP/2. For more information on this, please consult help documentation provided by the browser application vendor.