Specifically Californian fire retardants.
I find the idea that receipts are meaningfully poisonous to be laughable. You're in contact with them for a few seconds like once a week. Don't gargle the things and you're probably fine.
What if fire retardants are exactly as poisonous, i.e. not very? You're in contact with them for most hours every day. They're in essentially anything padded, including carpets. There's pounds of the stuff in every typical room, rather than the sub-gram amounts found in things like receipts.
Bonus: this is California we're talking, so inevitably fire retardants don't retard fires in realistic conditions. What they retard is lawsuits. (And, possibly, anyone sitting on them.) The smart thing to do would have been to stop selling to California, but of course Empire etc etc so instead everyone gets exposed to toxic anti-Californian-lawsuit chemicals.
The fire retardants are in the stuffing, not the upholstery. Not the surface that's going to be exposed to fire - which is a little good, since they're poisonous, but you're an idiot if you think they don't seep into the cloth over time. Plus the retardant only suppresses flame for about a dozen seconds. After that all it does is make the smoke poisonous.
I find packing foams often feel greasy. I expect that's the toxins in question.