In the film, which won the British star the Best Actor Academy Award at Sunday's (27Feb11) ceremony, Firth's stuttering monarch George VI is seen learning to overcome his speech issues by pronouncing rude words.
Officials at the Motion Picture Association of America's ratings board recently gave producers Bob and Harvey Weinstein permission to release a new family-friendly version alongside the existing R-rated version in cinemas at the same time.
But Firth has slammed the move - insisting the film should not be changed as the swear words aren't used in a "vicious" way.
He tells the Associated Press, "I don't take this stuff lightly, but in the context of this film, it could not be more edifying, more appropriate. It's not vicious, it's not an insult or it's not in any of the contexts which might offend people.
"Really, it's about a man who's trying to free himself through the use of certain words. I still haven't met the person who would object, so I think the film should stand as it is."