Snort 3.0 support is available to FDM/FTD6.7.0 and not yet available with FMC/FTD6.7.0.
https://www.cisco.com/c/en/us/td/docs/security/firepower/670/relnotes/firepower-release-notes-670/m_features_functionality.html#Cisco_Concept.dita_a80d279e-cfa6-4...