Liverpool played in front a redeveloped Anfield for the first time and they turned on the style versus Premier League champions Leicester City in a 4-1 win.
The Reds were playing their first Premier League home match of the season due to the work undertaken on the main stand, and Firmino brought the Anfield faithful to their feet with a cool 13th-minute opener.
Liverpool were unplayable at times and a stylish move resulted in Mane doubling their lead, only for a Lucas Leiva - deputising in defence for the injured Dejan Lovren - gaffe to tee up Jamie Vardy to half the arrears before the break.
It ultimately mattered little as a Lallana thunderbolt in the 56th minute extended the lead of Jurgen Klopp's side, with Firmino's second following a swift break completing the rout with one minute remaining.
Liverpool were one of just two teams to beat Leicester in their stunning title triumph last term and they now have six days to prepare for Friday's fixture with Chelsea, while the Foxes will attempt to return to winning ways in their Champions League opener at Club Brugge on Wednesday.
The home side gained an early foothold and deservedly moved in front when James Milner's pinpoint throughball was gathered by Firmino, whose excellent first touch took Robert Huth out of the equation and he calmly rolled his shot into the bottom left-hand corner.
The hosts were playing slick and after Daniel Sturridge was thwarted from eight yards by a brilliant Kasper Schmeichel save, Liverpool's pressure told in the 31st minute.
Sturridge raced onto Jordan Henderson's excellent pass over the top and produced clever backheel to pick out the supporting Mane, who made it eight goals in as many top-flight appearances with a dinked effort that was just too strong for Schmeichel's palm.
But Leicester were back in it before the break thanks to a gift from Lucas.
The Brazilian panicked under pressure from Shinji Okazaki and his pass towards Liverpool goalkeeper Simon Mignolet went straight to Vardy, who gleefully accepted the open goal.
Huth looped a header onto the crossbar from a long throw courtesy of substitute Luis Hernandez, who replaced the injured Danny Simpson after 34 minutes, as Leicester finished the half strongly.
The introduction of Ahmed Musa at half-time saw Claudio Ranieri's team press Liverpool high up the pitch, but Klopp's team restored the two-goal cushion in some style.
Mane pounced on Sturridge's deflected pass and held up the ball in the area before teeing up Lallana, whose stunning first-time effort rifled into the top-left corner.
At the other end, Mignolet - who finished the match with cotton wool up his nose and a plaster near his eye to mop up blood following a physical afternoon - was alert to prevent Vardy making it four goals in his past two appearances versus Liverpool with a smart one-on-one save with his legs.
Vardy continued to threaten for Leicester, but a late Liverpool break resulted in Mane beating the onrushing Schmeichel to the ball 40 yards from his goal before squaring for Firmino to side-foot into the unguarded goal.
Key Opta stats:
- Liverpool have won more games against reigning Premier League champions than any other side has (20).
- After winning three league games in a row at Anfield between 1997 and 2000, Leicester have failed to triumph in any of their last six there (D1 L5).
- Liverpool have scored more Premier League goals in 2016 than any other team (50).
- Jamie Vardy has bagged seven goals in his last eight Premier League matches.
- Since the start of last season Roberto Firmino has netted more top-flight goals than any other Liverpool player (12).