What kind of citrus tree??
It's a textbook example of the "Flying Dragon" cultivar of the trifoliate orange, Poncirus trifoliata. That particualr citrus cousing in extermely cold hardy, I've seen well established hedges of it growing outdoors in New York City, and there's a standard trifoliate tree growing outside of the main building of the Bronx Botanical Garden that's 20-30 feet tall. Edibility of the fruit (which should be slighty fuzzy) is debatable. They tend to be considered too sour or bitter to eat out of hand, but some people do use them to make marmalade.
Oh and if it is by some chance an Osage orange (it isn't, an Osage Orange that was big enough to have fruit would be too tall to get that kind of a picture, and they don't have thorns like that) the fruit while not edible is quite useful. apparenty it repels cokroaches