And he raised his parents upon the throne, and they fell in prostration before him; and he said: "Oh my father, this is the interpretation of my dream I had seen before, my Lord has made it a Truth. And He was certainly good to me when He delivered me out of the prison and brought you all here from the desert even though Satan had tempted between me and my brothers; indeed my Lord is compassionate to whom He Wishes, indeed He is the All-Knowing, the Wise".
‘They fell in prostration before him’ in this verse doesn't mean they did prostration just like they used to do before Lord. Instead, it means that they approved Yoosuf as the Messenger of Lord and decided to follow him in the Straightpath. Today's odd believers’ mode of prayer is explained in verses 7: 205-206. See explanation 2: 58; 3: 79-80 and 12: 4-5.