Firefox 78.15.0 ESR is the last version for Mac OS X 10.9/10.10/10.11 (distributionID: mozilla-mac-eol-esr1) and you will no longer receive updates. *https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr Firefox 78.15.0 on the Mozilla CDN server: *https://download-installer.cdn.mozilla.net/pub/firefox/releases/78.15.0esr/ Mac OS users on OS X 10.12/10.13/10.14 have been moved to the 115 ESR update channel (distributionID: mozilla-mac-eol-esr115), current releases require macOS 10.15 as a minimum. *https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support