Henderson rates the Brazilian highly despite him being unknown to the Liverpool captain prior to his arrival.
Firmino has since become the club's top scorer in all competitions this season, and has thrived under the management of Jurgen Klopp.
"He’s a very, very good player with a lot of skill who also works extremely hard for the team. He’s provided goals and I think he’s much more robust than people realise, he’s quite wiry.
"Now it’s about him continuing to grow and get even better."
The second half of the season in particular has seen Firmino grow - as he has managed to find the net on eight occasions since the turn of the year as he has been both leading the line for the club, as well as playing from a deeper role to support the main centre-forward.
As a result, the Brazilian is becoming and increasingly pivotal part of the side, and it's hard to think of Liverpool's best starting XI without him right now, whereas in the early stages of the season he was in and out of the side.
There are times when it seems that Firmino can go missing in games, but he can provide the sort of spark from nowhere that is either vital to the outcome of the game or can just get his side going.
Of course, there is plenty of improvement left in Firmino as Jurgen Klopp continues to develop his side, while Firmino is still only in his first season in England. But the early signs have been pretty good regarding the Brazilian and his Liverpool career.