Do native English speakers distinguish pines, spruces and firs in informal spoken English? Can it be that for most people they are just pine trees and people rarely use "spruce" or "fir" in their everyday vocabulary?
I think most English speakers are not necessarily knowledgeable enough about trees to be able to tell the difference between pines, spruces, or firs on sight, so in general people don't make that sort of distinction unless it's actually relevant to the conversation. When in doubt, most people will use "pine" as a generic term for most small/medium conifers, so that's what you'll hear most commonly when there isn't a need to distinguish what specific type something is.
That doesn't mean that somebody wouldn't use "spruce" or "fir" in informal speech if they did know that was the sort of tree they were dealing with, though, it's just most people aren't going to bother to find out just so that they can use the correct term. "Pine" is usually good enough.
The term "Christmas tree" is pretty much reserved only for trees which are used or are intended to be decorated or used in a festive context. Outside of the holidays, they're usually just called "pine trees".