The PowerShell command "New-SelfSignedCertificate" makes a better certificate than Makecert.exe. New-SelfSignedCertificate will create a certificate with a "Subject Alternative Name", which modern browsers check to validate the certificate. Without the SAN, modern browsers may show the certificate as untrusted even though in every other aspect it's perfectly fine. Makecert.exe cannot create the SAN.
If you're on Windows 7 and you have access to a Windows 10 machine, you could make the certificate using PowerShell on Windows 10 and then export it and load it on your Windows 7 machine. Another way to create a certificate on Windows 7 with a SAN is to use OpenSSL.
On Windows 10, open the PowerShell IDE and execute the following command to make the company certificate.