Serine hydrolase involved in the detoxification of formaldehyde. H2O + S-formylglutathione = formate + glutathione + H(+) 4-methylumbelliferyl acetate + H2O = 4-methylumbelliferone + acetate + H(+) Homodimer. There are two major electrophoretic isotypes. The sequence of the ESD*1 variant is shown (PubMed:12721789, PubMed:7907313). Belongs to the esterase D family.