I was recently fired from my job for "receiving a counterfeit bill".?

Every bill you have to mark? Or do you mean every bill you suspect of being counterfeit? Is there such a thing as a pen that detects counterfeit bills? I know a firm that fines their employees for accepting counterfeit bills, but they don't fire them. What sort of work do you do? I hope you can sort this out, it sounds outrageous.