No I don't think this is normal. Do they have cubs at the moment? If so then I believe adults will sometimes regurgitate food for their young - part digested and prechewed! Maybe they would make a choking/retching sound when doing this? Other than that it may be bad news. Foxs, like dogs, can get a viral distemper. This is serious, infectious and often fatal. Symptoms include a dry cough (choking).
havent seen any cubs but i usually hear them in the dead of night and the cubs could easily be in the bushes and trees. Is it wrong to leave food for them?
It's up to you about the food. I have a fox and a badger that come into my garden every night. Rather than throw away food scraps I put them out and they're polished off very quickly. In my experience a fox will eat almost anything. Badgers on the other hand absolutely hate vegetables (they can even separate peas out from a plate of leftovers) but love pasta and anything fatty! Foods to be wary of: cooked bones (they splinter unlike uncooked bones), dairy products (too much causes upset stomachs) and chocolate (as with dogs, chocolate is poisonous to foxs).