What details are given in "The Hearth and Salamander" make you think this story might be set in the future?
The flameproof jacket mentioned on the second page was somewhat futuristic in the early 1950's when the book was written. The air-propelled train mentioned in the next paragraph is also something that puts the story in the future. Clarisse's conversation with Guy reveals futuristic elements especially as she asks him about his job as a fireman: does he ever read any of the books he burns; is it true firemen once put out fires as opposed to starting them; it's unusual for a house not to be fireproof; her uncle arrested for driving too slowly at 40 mph; parlor walls being watched. Much information about the setting and the society are given through Clarisse as she talks with Guy. The technicians who come to pump out Mildred when she has taken an overdose of her pills are also futuristic. There is even a description of a toaster that butters Montag's bread for him. Mildred's description of her TV shows and how they are interactive are also elements of a setting in the future. The mechanical hound at the firestation is also futuristic. In a later conversation, Clarisse talks with Guy more about their society, especially about other people her age and how they act. All of this gives the reader a clear idea that the setting is some vague, not too distant future. And that's only about 30 pages into the book.