Newer versions of Firefox (released after version 79.0) require macOS 10.12 Sierra or higher, meaning modern updates will not install on a Mac running Yosemite 10.10.5.
May 2026 Reading Time: 6 minutes
or other community-backported browsers, though upgrading your macOS is the only way to get a fully secure Firefox. Mozilla Support compatible browser
If you are using a legacy Mac running 10.10.5, installing the proper legacy build is necessary to maintain standard web compatibility. This comprehensive document guides you through downloading, installing, and optimizing Firefox for your OS X Yosemite system. 🛠 Official Facts vs. Misleading Claims firefox download for mac 10105 upd
For users running , the most recent and final compatible version of Firefox is Firefox 78.15.0 ESR (Extended Support Release) . This version reached its final update on October 5, 2021, and is no longer receiving security patches from Mozilla. Download Instructions
You can download the English (US) installer directly from the Mozilla CDN. File Name: Firefox 78.15.0esr.dmg
Wait for the copy tracker bar to finalize. Once done, unmount the setup drive by right-clicking the Firefox disk icon on your desktop and selecting . Newer versions of Firefox (released after version 79
Do not panic. Your machine is not obsolete yet. This guide will walk you through everything you need to know about locating, downloading, and installing the for Mac OS X 10.10.5 Yosemite, why you need the specific Extended Support Release (ESR) , and how to perform the update safely.
Select your preferred language folder (e.g., en-US/ for US English).
Many modern websites rely on web standards introduced after 2021. If a site like YouTube or Amazon looks scrambled, it is likely due to outdated JavaScript processing or unsupported CSS attributes. If you encounter layout issues, click the in the address bar to adjust your Enhanced Tracking Protection settings, as strict settings can sometimes block older script styles. Security Warnings and SSL Certificates This version reached its final update on October
Running macOS 10.10.5 in 2026 is risky. Even with an "updated" Firefox 78, the OS itself is vulnerable.
Open your current browser (even Safari 11) and navigate to: