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.
Mozilla Firefox For Mac 10.5.8
Download Firefox For Mac Lion; Fixed an issue in Mac OS X 10.7 that could cause Firefox to crash; Fixed an issue caused by Apple's 'Java for Mac OS X 10.6 Update 5' where the Java plugin would not be loaded. End-of-life 5.0. Mozilla Firefox (or simply Firefox) is a free and open-source web browser developed by Mozilla Foundation and its. Download Mozilla Firefox, a free Web browser. Firefox is created by a global non-profit dedicated to putting individuals in control online. Get Firefox for Windows, macOS, Linux, Android and iOS today!
If you're using an outdated version of Firefox on Mac OS X 10.8 (Mountain Lion) or earlier, the only way you can update Firefox to a secure version is to upgrade your Mac OS to a version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.
Firefox For Mac Os 10.7
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.