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.
Apple also released the 10.6.8 update for Mac OS X Snow Leopard Server. Among other things, it fixes issues displaying videos in Wiki pages for Firefox and Internet Explorer, improves the. Firefox の OS X 10.6、10.7、10.8 に対するサポート終了について 重要 - macOS 10.9、10.10、10.11 ユーザーの拡張サポートリリースへの移行 Firefox を Mac へインストールする. 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.x product line on August 16, 2011. 6.0 August 16, 2011 Official Firefox 6.0 release. About:permissions, a.
If you're using an outdated version of Firefox on Mac OS X 10.8 (Mountain Lion) or earlier, the only way you can update Firefox to a secure version is to upgrade your Mac OS to a version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.
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.