Starting with Firefox version 49, Firefox requires Mac OS X 10.9 (Mavericks) or higher. Visit this Apple Support page to find your Mac OS version.
If you're using an outdated version of Firefox on Mac OS X 10.8 (Mountain Lion) or earlier, the only way you can update Firefox to a secure version is to upgrade your Mac OS to a version that Apple supports. Visit this Apple Support page to learn more about upgrading your Mac.
Mac Os Version Upgrade Version
While insecure versions of Firefox will continue to work on OS X 10.8 and earlier, using an up-to-date version of Firefox on a supported version of Mac OS will provide you with the best and safest user experience.
Mac Os Version Upgrade Windows 10
The Apple Support Downloads page is most useful for finding software for more recent older Macs, particularly anything that is running a version of Mac OS X, even if it’s no longer a supported or updated system software release, like for Macs running Mac OS X Tiger 10.4 or Mac OS X Snow Leopard 10.6.5. Download Mac OS X 64-bit/32-bit x86-64/i386 Installer; Python 2.6.9 - Oct. No files for this release. Python 3.3.2 - May 15, 2013. MacOS Big Sur elevates the most advanced desktop operating system in the world to a new level of power and beauty. Experience Mac to the fullest with a refined new design. Enjoy the biggest Safari update ever. Discover new features for Maps and Messages. And get even more transparency around your privacy. Check what version of OS X or macOS your Mac supports. The latest version of macOS, macOS Catalina, is supported on any Mac introduced in 2012 or newer. If your Mac doesn't support macOS Catalina, it might be supported by macOS High Sierra, which requires a Mac introduced in 2009 or 2010. If your Mac isn't supported still, you could still.