This is how you set a Ge interface on a Juniper device disable auto MDI-X negotiation as well as set the speed on the interface to 1Gbps.

set interfaces ge-0/0/1 ether-options no-auto-negotiation
set interfaces ge-0/0/1 ether-options link-mode full-duplex
set interfaces ge-0/0/1 ether-options speed 1g