Doing some testing with SSL Deep Inspection with FortiOS 6.4.6 and getting this error on Firefox (89.0.2) when connecting to Facebook:
Certificate is imported correctly on the Win7 PC, and I do not get the error when using Chrome. I have verified in the Browsers that the Fortinet SSL certificate is being used. Other websites like Reddit are working correctly in Firefox with the Fortinet certificate. If I add Facebook to the Exempt addresses, it works correctly on Firefox.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.