Firefox 79.0 to 115.0 ESR requires macOS 10.12 (ten.twelve) at minimum to run while Firefox 116.0 and later requires macOS 10.15 at minimum to run. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support The most current Firefox you can run on the old EOL macOS 10.9, 10.10, 10.11 is Firefox 78.15esr which you appear to have according to your More system details on right. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr