Import all the certs in the chain into the firewall. It will 'know' they are all part of the chain, find them, and it should work.
Let's say the diagram on this page is your setup.
Can you try importing the top cert AND the middle cert as firewall certificates? Then import the middle and bottom certs as CAs. Maybe you have to import the 'root CA' as a firewall cert too, I am not sure, but you can test this quickly and let us know.
Yep - That is how the certificate chain is laid out. I already did have the intermediate certificates installed under the CAs.
I can't install the intermediates as full "firewall" certificates since I don't have the private keys for them. I am just guessing that DigiCert won't give them to me (Sorry - bad public key cryptography humor.)
Demand their private keys from them! Ok I thought you were just testing this out with some certs you had layin' around ...
I've asked some beings higher-up in the knowhow tree and we'll wait for an answer from them.
As you know through the ticket you filed the firewall cannot present intermediate certs when doing SSL decryption. It can only present the one cert you select in the SSL Rule.