Firmino has been a revelation in an attack-heavy side under Markus Gisdol and the Liverpool target aided the triumph with an assist.
But the goals came from Eugen Polanski, Anthony Modeste and Sebastian Rudy with Hannover going down to 10 men later in the game after Manuel Schmiedebach's dismissal.
Hoffenheim's fluid attacking side with Firmino, Modeste and Kevin Volland has caught the eye this season, but they had to come back from a goal down as Leon Andreasen netted for Hannover on eight minutes.
Andreasen completed a neat one-touch move with the killer pass coming from Leonardo Bittencourt to set up the midfielder who tucked home.
Six minutes later, Polanski volleyed Hoffenheim level from the edge of the penalty box.
With neither side locked in a battle for Europe, nor a relegation dogfight, there was little resting on this encounter in Sinsheim.
Gisdol's side took the lead on 51 minutes through French striker Modeste who broke the Hoffenheim offside trap and finished Firmino's through ball.
Germany Under-21 international Rudy came close on 57 minutes with a fierce 30-yard strike which forced Ron-Robert Zieler into a superb save.
Hannover were reduced to 10 men after 75 minutes when Schmiedebach was shown a straight red card after a two-footed lunge on Modeste.
Rudy did get his name on the scoresheet, though, in the final minutes, finishing from the same distance after Zieler mis-kicked straight to the Hoffenheim midfielder's feet.