He has 25 goals and 14 assists in 47 games for the club in every competition.
"He has his own style and that makes him special," the ex-Netherlands international told the club's website.
"That's what I like in players. A typical goalscorer or different kind of striker, you see that a lot in Europe, but Firmino has his own style and he has his own speciality; he is scoring great goals but also feeding the players around him.
"He's a great goalscorer but he's also a team player in everything he does. I don't know him quite well, but if I see him playing then he just wants to win with the team and he's not the type of player who wants to score for himself. That, for me, is the biggest thing of Firmino.
"He's scoring great goals but he's also giving great assists and then you are, in my eyes, a complete player who is a great thing for Liverpool."