The last security update applicable to OS X 10.11 was made available in July 2018. While Apple does not have a public policy governing security updates for older OS X releases, their ongoing practice has been to support the most recent three releases. Why has Firefox ended support for OS X 10.9, 10.10 and 10.11 users? This will provide security updates until the next ESR update in July 2021, after which the affected users will no longer receive security updates. These users will be moved to the Firefox Extended Support Release (ESR) channel by an application update. Firefox Mac OS X 10.9, 10.10 and 10.11 users move to Extended Support Releaseįirefox version 78 is the last supported Firefox version for Mac users of OS X 10.9 Mavericks, OS X 10.10 Yosemite and OS X 10.11 El Capitan.