Currently, the certificate details of an S/MIME certificate look like this:

We want to add the serial number here, as it is (together with the issuer) the unique identifier for an S/MIME certificate. Please add the hexadecimal serial number below the issuer ("Serial number")

And please move the position of the fingerprint to directly above "Private key" (if it's not to complicated), as it is less important info for an S/MIME certificate (we only use it internally and it may change).