Had Firefox update 78 for my Mac, operating sys. OS X El Capitan 10.11.8.. tried to update to 91. After update found out 91 would not work on my OS X. Npw I don't have Firefox and can't find Ver 78? help!
Firefox 79.0 and later has required MacOS 10.12 at minimum to run so you will need to upgrade to macOS 10.12 or higher in order to run Fx 94.0.2 and 91.3.0esr
Fx 78.15.0esr can be found at https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/en-US/ other locales are at https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/