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.
Open the Thunderbird download page. The page will automatically detect the platform and language on your computer and recommend the best edition(s) of Thunderbird for you. If you want to download Thunderbird in a language other than the one suggested, click on 'Other Systems & Languages' for the list of available editions. Jun 14, 2012.
Mozilla Firefox For Mac
If you're using an outdated version of Firefox on Mac OS X 10.8 (Mountain Lion) or earlier, the only way you can update Firefox to a secure version is to upgrade your Mac OS to a version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.
Mozilla Firefox 41 Setup Download
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.