Mozilla will end support for Firefox on OS X 10.6, 10.7, and 10.8 in August, 2016. At that time, Firefox will continue to function on these platforms but will no longer receive new feature or security updates.
Firefox Extended Support Release (ESR) 45 will continue to support OS X 10.6, 10.7, and 10.8 until mid-2017, but this ESR release will be the last that supports them.
All three of these versions are no longer supported by Apple. Mozilla strongly encourages our users to upgrade to a version of OS X currently supported by Apple. Unsupported operating systems receive no security updates, have known exploits, and are dangerous for you to use.