Bishops Mitre hat hunt/livery circa, made by FIRMIN circa 1875-85

Large dished back 25mm brass button by “FIRMIN & SONS LD ★ LONDON” with no street address stamped in.  since the “Ltd” confirms it’s after 1875, but there’s no St Martin’s Lane or Cork Street address (which start appearing from 1894), this points to a manufacture window of roughly 1875 to the early 1890s — i.e. the plain “Firmin & Sons Ld, London” mark used in the gap between adopting “Ltd” and the firm starting to stamp their specific address onto buttons.