Getting fired for preaching at your secular job is not persecution.
If there’s nothing in your job description about preaching to co-workers or where applicable, customers, don’t do it.
If you’re not going to do the job that you’re paid to do, and if you’ve had prior warnings regarding the matter, your boss has every right to fire you and replace you with someone who will do what is expected of them without a fuss.
Do your job and leave your god at home where it belongs.
If you can’t do your job, find another one.