First, can your employer fire you? Answer is probably yes (but I am not a lawyer, and did not stay at a Holiday Inn Express last night). With the exception of certain protected rights (I cannot fire you because you are a Baptist, vote for Ron Paul, or file a complaint with OSHA) or a written contract, MOST employees are employed "at will". If they want you gone, they CAN tell you to go. For any reason, or no reason.
Second- Felon and firearms. The felon may not have uncontrolled access to firearms. That means when he is around a gun, it is either ON someone, or under lock and key (and he does not have access to the key).
Can't tell you what you should do- call you have to make. Not gonna talk about Ida Dunn (Well, Ida Dunn gone upside his head with a chair, etc)
What we have here is... failure- to communicate.