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.
citation needed AppleWorks will not run on any versions of Mac OS X later than Snow Leopard because it is compiled for the PowerPC CPU architecture. 19 AppleWorks word processing, spreadsheet, and presentation files can be opened in earlier versions of iWork applications Pages, Numbers, and Keynote respectively, but not since 2013. AppleWorks is an integrated office suite containing a word processor, database, and spreadsheet. It was developed by Rupert Lissner for Apple Computer, originally for the Apple II platform and launched in 1984, and was later reworked for the Macintosh platform. The Apple subsidiary Claris created the new successor ClarisWorks for Apple IIGS, Macintosh, and Windows. Those applications do not share any.
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.
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.
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.