Firefox 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. These users will be moved to the Firefox Extended Support Release (ESR) channel by an application update. This will provide security updates until the next ESR update in July 2021, after which the affected users will no longer receive security updates.
Why has Firefox ended support for OS X 10.9, 10.10 and 10.11 users?
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. The last security update applicable to OS X 10.11 was made available in July 2018. Unsupported operating systems do not receive security updates, have known exploits and can be dangerous to use, which makes it difficult to maintain Firefox on those versions.
Can I still browse safely with Firefox on OS X 10.9, 10.10 or 10.11?
Up until July 2021, we will be updating affected users with critical security updates through the Firefox ESR channel to help retain the best possible security. After this, no security updates will be provided.
How can I get the newest features of Firefox?
If you want to keep your Firefox version up to date, you will need to upgrade your operating system to macOS 10.12 or higher. Older versions that are not supported by Apple are unreliable and unsafe to use, which also makes it difficult to maintain Firefox on those versions.