People sometimes complain that their home fire safe stinks and it makes the contents smell bad, too. This is caused by leaving the safe closed for long periods of time, especially when it is moist inside.
1) All safes should be opened every two weeks or so to let the old air out. This is especially true with new units because the poured-in insulation may not yet be completely dried. Just leaving the door open for several weeks might get the smell out.
2) Clean the inside of the safe with detergent or bleach. Then enclose one or two laundry drier sheets inside. We use Bounce/Febreze and it normally fixes the problem.
3) If the smell persists there is probably mildew growing in the insulation. We have had success by putting a bowl of bleach in the safe and closing the door for a week. It seems like fumes from the bleach kill the mildew.
4) Still got a problem? Buy a new safe and open it regularly.