It appears you are using macOS 10.10 so the most current Firefox you can run is Fx 78.15.0esr. Firefox 78.15.0esr is the latest to still support the old EOL macOS 10.9, 10.10, 10.11 https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr Firefox 79.0 to 115 ESR requires macOS 10.12 (ten.twelve), 10.13, 10.14 at minimum to run. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support Firefox 116.0 and later requires macOS 10.15 (ten.fifteen) or later to run. If you can update to at least macOS 10.12 (ten.twelve) then you can use the still supported Fx 115 ESR (currently at 115.8.0esr) as the last update 115..15.0esr will be in Sept 2024. https://www.mozilla.org/firefox/all/#product-desktop-esr (<--requires macOS 10.12 or later as it will not run on your macOS 10.10)