So tossing a few oranges or whatever from time to time probably won't do anything harmful at all. When I have an orange with a bad spot, I cut off the bad spot, slice up the rest and toss it out to the chickens. they love it. I give them all kinds of fruit and veg, they don't usually eat the onions, though. They didn't care for raw turnips, but liked the greens. Sometimes they will eat the green part of scallions. I feed them potato peels. I feed them beans and peas, but only cooked ones. They lay egg and are active and healthy.
I wonder how many of these things we're told are "bad for them", are the results of experiments that involve feeding much larger amounts than most people are likely to have on hand as scraps? I really have never found any food (that chickens liked) to have ill effects on my birds. It probably would be bad to feed them huge amounts of potato peels and oranges, though! It would also be bad to feed them huge amounts of corn and oats, if they didn't have enough other things to balance it.
I've read not to feed them large amounts of salty foods, that they can get salt poisoning. I think that one's probably valid. People and other animals can die from too much salt, too. So I wouldn't give them large amounts of canned veggies that contain salt, salty snacks like chips, but a nibble now and then wouldn't hurt, I'm sure. I wouldn't give them brine from pickle-making or anything similar.