The long “s” (∫) was common in print in Europe from the 15th to the 18th centuries. Language writer, Ben Zimmer, was looking for the earliest references to “seersucker,” but he found that his searches were hobbled by the problem of optical character recognition mistaking the long “s” for a “f” in older texts. He searched instead for “feerfucker” and discovered late 17th century references that predated the earliest citations in the Oxford English Dictionary. You can hear the tale on the Lexicon Valley podcast. And although they varied a bit from one language to the next, there were rules on where the “∫” was placed in text. Apparently, confusing the “∫” with the “f” was not a problem in the three hundred years in which the long “s” was in common use.