Firefox since 116.0 and later including the current versions requires macOS 10.15 (ten.fifteen) or later to run. For macOS 10.12, 10.13, 10.14 the most current you can run is Firefox 115 ESR. It is currently at Firefox 115.19.0esr and will be updated til Fx 115.21.0esr in March 2025 unless Mozilla decides in next while to extend updates again. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support The Firefox 115.19.0esr.dmg can be downloaded from below. https://archive.mozilla.org/pub/firefox/releases/115.19.0esr/mac/en-US/ Folders for the other languages are at https://archive.mozilla.org/pub/firefox/releases/115.19.0esr/mac/