Catalyzes the transfer of a formyl group from 5-formyl tetrahydromethanopterin (5-formyl-H(4)MPT) to methanofuran (MFR) to produce formylmethanofuran (formyl-MFR) and tetrahydromethanopterin (H(4)MPT). 5,6,7,8-tetrahydromethanopterin + H(+) + N-formylmethanofuran = methanofuran + N(5)-formyl-5,6,7,8-tetrahydromethanopterin One-carbon metabolism; formaldehyde degradation; formate from formaldehyde (H(4)MPT route): step 4/5. Homotetramer. Belongs to the FTR family.