Could a smoker who works at a fireworks factory refuse to go outside on their cigarette breaks and be protected from firing?
no, smoking is not protected the same way religion isNo duh, but so what? You're freely allowed to believe in whatever religion you want, and you obviously shouldn't get fired on the basis of your religion, but the first amendment doesn't mean that you are entitled to a job if you are incapable of doing said job. If I started a religion named Koopism where my believers are completely barred from washing their hands lest they face eternal torment in the 7th Circle of Hell, should I be allowed to work in a kitchen? Or for a less extreme example, what if Koopism forbade its followers from touching dead animal meat? Should a Koopist be entitled to work at McDonald's even though they would be unable to cook anything besides hash browns and freedom fries?
