Post Office - Firth 323 N Main St Firth, ID 83236 Phone : (208) 346-6611 Post Office - Firth Business Category Post Offices Toll-Free           (800) ASK-USPS Fax           (208) 346-4132 United States Government--postal Service, Firth 323 N Main St Firth, ID 83236 Phone : (208) 346-6611 United States Government--postal Service, Firth Business Category Government Offices-Federal Government Offices & Public Schools