The Dutchman was confirmed as a Liverpool player in the final few days of 2017 after an initial transfer fell through last summer.
Jurgen Klopp could hand Van Dijk his debut in Friday's FA Cup third-round clash with Everton at Anfield and Firmino is excited to step out on to the field alongside him.
Firmino has hailed the quality of the former Southampton man and feels he will help them in their pursuit of a top-four spot.
"He's a really, really good defender. It's always really hard playing against him. It's very hard, he marks very tightly and I just think he's a really, really high-quality player," Firmino told Liverpool's official website.
"I think in addition to the fact he's very physical, it's his presence. He's tall, he's very strong and that's in addition to his innate ability.
"I just hope he helps us as much as possible. I think like everybody else who comes in, they add something to the group and I hope that he can also do that and bring something to the team himself.
"I'm really looking forward to playing alongside him, of course.
"Obviously it's great that he's joined our team and now that he's come with us of course I'll welcome him in with open arms and I'll look to make friends with him."