Aha! Finally found the answer to the bothersome question of why antique manuscripts used “f” for final “s”.
Insular Hand…

Several of the Roman letters, notably f, g, r, s, and t had distinctive shapes. S indeed had three alternate shapes, oen of which, called long s, looks very much like an f in modern typography except that the horizontal stroke does not go through to the right of the letter. This particular variant of s (f) was used until the end of the eighteenth century save in final position, printers following what was the general practice of the manuscripts.—The Origins and Development of the English Language, Thomas Pyles and John Algeo