If you decide to disable HTTP/2 in IIS on Windows Server 2016 and only use HTTP/1.1, you can do so by adding two DWORD registry keys. You can copy the text in the box below into an empty Notepad file and save it as a .reg file. Then double-click the file to import the registry keys and reboot.
Windows Registry Editor Version 5.00
If you decide to enable HTTP/2 at a later time, you can either delete the two registry keys or change their values to 1.
If you’re trying to browse to a website and you’re getting the error NS_ERROR_NET_INADEQUATE_SECURITY in Firefox and you’re not an administrator of the server, you can disable HTTP/2 in Firefox.