Firmino missed Liverpool's last three games but took part in a group training session on Monday, photos on the club website showed. The Brazilian has six goals and five assists in 27 league games this season.
Liverpool are still without central defenders Virgil van Dijk, Joe Gomez (both knee), Joel Matip (ankle) and midfielder Jordan Henderson (groin) due to injuries.
Liverpool won their first English top-flight title in 30 years last season but injuries and poor form has left them seventh with 46 points, 25 behind leaders Manchester City.
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Home/Sports/Football/Liverpool's Firmino Back In Training Ahead Of Arsenal Trip