The rather ancient macOS 10.8 was released way back on July 25, 2012 and the last update 10.8.5 was released on August 13, 2015. For macOS 10.9, 10.11, 10.11 that last Firefox version to still support was the old eol Firefox 78.15.0esr. For the even older macOS 10.8 the most updated version of Firefox to support was the old eol Firefox 45.9.0esr https://archive.mozilla.org/pub/firefox/releases/45.9.0esr/mac/en-US/ other language locale folders at https://archive.mozilla.org/pub/firefox/releases/45.9.0esr/mac/ Firefox 45 is old and vulnerable and many current websites may not work or at all but then that could be said about any web browser version that last support the old macOS 10.8.