Mac OS X Lion (version 10.7) is the eighth major release of macOS, Apple's desktop and server operating system for Macintosh computers. A preview of Mac OS X 10.7 Lion was publicly shown at the 'Back to the Mac' Apple Special Event on October 20, 2010. 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.
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If you're using an outdated version of Firefox on Mac OS X 10.8 (Mountain Lion) or earlier, the only way you can update Firefox to a secure version is to upgrade your Mac OS to a version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 Windows 10
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.