Full MX104 will have system licenses installed to activate the onboard 10G ports.
cmyers@lab-mx104-1.re0> show system license License usage: Licenses Licenses Licenses Expiry Feature name used installed needed scale-subscriber 0 1000 0 permanent scale-l2tp 0 1000 0 permanent scale-mobile-ip 0 1000 0 permanent MX104-2x10Gig-port-0-1 0 1 0 permanent MX104-2x10Gig-port-2-3 0 1 0 permanent Licenses installed: License identifier: <deleted> License version: 2 Features: MX104-2x10Gig-port-0-1 - MX104 2X10Gig Builtin Port(xe-2/0/0 & xe-2/0/1) upgrade permanent MX104-2x10Gig-port-2-3 - MX104 2X10Gig Builtin Port(xe-2/0/2 & xe-2/0/3) upgrade permanent
If I remember correctly, the onboard 10G ports on the MX104 aren't even visible until the license is applied; there was another forum post on that a year or so back.
-Chad