Green was jailed last November for four years on charges including aggravated robbery, unlawfully discharging a firearm, unlawfully possessing a firearm and shoplifting.
At yesterday's sentencing, Crown prosecutor Bernadette O'Connor said there was no difference between Firth and Green in terms of the level of involvement in the robbery, noting the Court of Appeal had said that a getaway driver during a crime may be the ringleader.
At this stage, a man from the public gallery blurted out "bull****" which prompted Judge Greg Davis to order that the comment be withdrawn or the man leave the court.
Ms O'Connor said Firth had 42 previous convictions compared to Green's 14.
Firth, she submitted, was sentenced to nine months in jail in 2007 on a charge of unlawfully carrying a firearm.
His lawyer, Kelly Ellis, said Firth was remorseful for his actions which was evident by his early guilty plea and a letter he wrote to the dairy owner.
Judge Davis said the robbery had had a pronounced effect on the shop attendant as she was now more cautious of people around her.
He sentenced Firth to three years and nine months on the charge of aggravated robbery and a concurrent term of one month for drink driving.