Fir's foliage, when crumbled in your hands, smells like lemons. Spruce smells like your typical x-mas tree.
And as said above Fir is F for Flat
Spruce is S for Square. In our area theres only 3 really. Fraser (which arent that common mostly planted), Balsam, and White. You will see SOME Dougs but they were planted. Balsam and Fraser have a REALLY smooth bark, Whites have long flat needles that almost look like a blue spruce. Frasiers are a lil tougher, as they look identical to Blasam, but they are so rare up here, unless planted..................