Jurgen Klopp's side are now a whopping 16 points ahead of second-place Leicester City – who lost to Southampton earlier in the day – although their lead at the summit could be cut to 14 points if Manchester City overcome Aston Villa on Sunday.
The Reds were dominant in the first half and made the most of their superiority when Firmino expertly drilled home from inside the penalty area after 37 minutes.
Son Hueng-min and Giovani Lo Celso squandered golden opportunities to snatch a scarcely deserved point for Jose Mourinho's men late on, with Liverpool ultimately holding on for yet another three points.
Liverpool twice came agonisingly close to going ahead inside two minutes. Firmino's initial effort was cleared off the line by top-flight debutant Japhet Tanganga, with Alex Oxlade-Chamberlain lashing against the post from the follow-up.
Lucas Moura, Son and Dele Alli all missed the target from promising positions soon after, while at the other end Virgil van Dijk headed straight at Paulo Gazzaniga from just six yards.
There was little the Spurs goalkeeper could do to deny Firmino eight minutes before the interval, the Brazil international controlling Mohamed Salah's pass with a sublime touch before lashing in from 10 yards.
Spurs started the second half with a spring in their step and twice came close before the hour mark, with Serge Aurier testing Alisson and Son seeing an effort deflected narrowly wide.
The game was almost put out of their reach in the 66th minute but Gazzaniga got down sharply to paw away Sadio Mane's header.
Spurs rallied in the closing stages, with Son blazing over from a glorious position and substitute Lo Celso somehow diverting Aurier's cross wide from inside the six-yard box seven minutes from time.
Klopp was visibly furious at his side's defending, but it mattered little in the end as they held on for a win that strengthens their already formidable position at the summit.
What does it mean? Relentless Reds march on
Klopp's men have now taken a scarcely believable 88 points from their last 90 available in the Premier League, winning their last 12 matches in a row.
They rarely looked in danger of failing to claim all three points against a Spurs side desperately missing the presence of the injured Harry Kane in attack.
Mourinho, meanwhile, needs to turn his side's fortunes around sharpish. They have now won just one of their last five Premier League games and are nine points behind fourth-placed Chelsea.
Firmino's touch of class
Mane and Salah often steal the headlines, but Firmino once again proved his worth with a superb goal. His first touch was exquisite, and the finish was not bad either. He also created four chances for his team-mates.
Eriksen's Spurs career ending with a whimper
With a move to Inter seemingly on the cards, it was a surprise to see Christian Eriksen named in Mourinho's starting XI.
Despite creating a few chances, he failed to repay his manager's faith, serving up a dismal display where he was often outmuscled and appeared to be lacking intensity.
What might be one of his last appearances in a Spurs shirt ended with a 69th-minute substitution.
Tottenham host Middlesbrough in an FA Cup third-round replay on Tuesday before visiting Watford in the Premier League on Saturday. Liverpool, meanwhile, welcome bitter rivals Manchester United – the only side they have dropped points against this season – to Anfield on Sunday.