The last security update applicable to macOS 10.11 was made available nearly 2 years ago in July 2018 ( ). While Apple doesn’t have an official policy governing security updates for older macOS releases, their ongoing practice has been to support the most recent three releases (i.e.
On June 30th, macOS 10.9, 10.10 and 10.11 users will automatically be moved to the Firefox Extended Support Release (ESR).
