Do we have a list mentioned inbound Messaging SSL CA Certificates. Does SFDC Domain support Extended EV for SSL inbound?

Hello,

for our community we have uploaded a Digicert Certificate to Salesforce and connected to our domain. Once we open our site, it works for most of the browsers. But not for FireFox and mobile device browsers. We completed the following test:

https://www.digicert.com/help/index.htm?host=success.ressoftware.com

The final check is not good (The server is not sending the required intermediate certificate.) This is all within the Salesforce environment. What is wrong with this certificate? Should we upload another one, or must something be adjusted on the Salesforce server?

Thank you for your response.