Your tongs were made by François-Joseph Meresse, a buckle maker (la boucle) working in Paris at 100 rue de la Verrerie. He registered his mark FJM, symbol a fly (une mouche) in 1798. No end date is given.
See Arminjon, v. I, no. 01152, p. 142.
In addition to the maker’s mark you have the silver standard mark of a cock in an octagonal reserve for 950 silver, and a guarantee mark of a man’s head in a circular reserve, both for Paris, in use from 1798-1809. Also there is another mark that is difficult to make out to the right of the maker’s mark. Perhaps a later recount mark?
Hope this helps.