But the 49-year-old actor admits he hates Christmas and is more like Scrooge than the character he portrays in the movie - Ebenezer's impossibly cheerful nephew, Fred. 'I have a profound loathing of Christmas - it's sad really,' he confesses.
'At this time of year, I am careful not to switch on the radio because those novelty jingles make me homicidal and plunge me into the heart of Scrooge territory.
Admirabel anti-hero: Jim Carrey stars as the miserly Ebenezer Scrooge in Disney's Christmas Carol
'I think A Christmas Carol is the best seasonal story you'll find, because after its darkness, fear and regret, you're ready for a bit of joy by the end.'
While Scrooge is described by Dickens as 'hard and sharp as flint, from which no steel had ever struck out generous fire; secret and self-contained and solitary as an oyster', Firth admires his single-mindedness and his bracing cynicism.
'Scrooge is an anti-hero, for some reason - people admire this terrible old curmudgeon,' says Firth, who became a national treasure as Mr Darcy in the 1995 BBC adaptation of Pride And Prejudice.
'Kids may be scared of the story, but you have to tell them it has a happy ending and that the ghosts are, in fact, acts of kindness to encourage Scrooge to change.'
And despite special-effects which make the snowflakes drift so close you can virtually feel them, Dickens purists may be pleased that, of all the versions of his story, Disney's is probably the one that most closely resembles the author's text.
• A Christmas Carol is released in cinemas today.