Can a former employer inform a prospective employer about the reasons for an employee being fired?

Generally yes, as long as it is factually accurate, there are not federal laws that restrict what an employer can state about their former employee to a prospective employer. So if you were fired, then your former employer can certainly notify your new employer of that fact, also if you were fired for employment misconduct, for example fraud or stealing, then your former employer can say so as well. However, if your former employer says something that is not truthful, you may be able to sue them for deformation.