https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support Firefox 116.0 and later including the current Firefox 146.0.1 Release and 140.6.0ear requires macOS 10.15 (ten.fifteen) or later to run. For the eol macOS 10.12, 10.13, 10.14 the most current Firefox you can run is Firefox 115.31.0esr unless you can update your macOS to 10.15 or newer. /moved thread from Firefox for iOS (iPhone/iPad) to desktop Firefox section as you have macOS.