The former Brazil star has urged Jurgen Klopp to build his Liverpool team around his compatriot, who has started to find his best form since the German took over at Anfield
Liverpool paid £28.7 million to sign Firmino from Hoffenheim in the summer and after a slow start to life in England, he has now started to repay the Reds's investment.
The 24-year-old, who was often been used as a centre forward this season, has found the net five times in the Premier League - with four of those coming in his last four games - and contributed five assists.
"I didn't ever question if he would be a great player for Liverpool, I knew that he would be," Ronaldinho told the Daily Mirror.
"He's one of the best at what he does in the world. He's in the same class as Ozil, [David] Silva, Iniesta, and all the other great players who play that role.
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"He's the player that I'm sure Klopp will build his new Liverpool team around.
"Klopp is one of the best coaches in the world, he will know that Liverpool need better players, he will know that Firmino will need better players around him to get the most out of his game.
"I'm sure when he joined Liverpool, Klopp was promised he could bring in his own players, and with Firmino at the centre of the team, there's no reason Liverpool cannot challenge once again."