Enables farnesyl-diphosphate farnesyltransferase activity. Involved in cholesterol biosynthetic process and farnesyl diphosphate metabolic process. Located in endoplasmic reticulum membrane. Used to study cataract. Orthologous to human FDFT1 (farnesyl-diphosphate farnesyltransferase 1). [provided by Alliance of Genome Resources, Apr 2022]