Mossner was born on October 22, 1907, in New York City. He received his bachelor's degree in English, Latin and history from City College of New York in 1929, and his master's and PhD degrees in English and Comparative Literature from Columbia University in 1930 and 1936.
Mossner was born on October 22, 1907, in New York City. He obtained a bachelor's degree in English, Latin, and history from City College of New York in 1929, followed by a master's and PhD degrees in English and Comparative Literature from Columbia University in 1930 and 1936.