Even though Firefox generally runs smoothly on macOS 10.15, you may encounter occasional issues. Here are some common problems and their solutions.
While Firefox 78 ESR keeps your computer functional, it is important to know its limitations in 2026:
Many websites will trigger connection warnings because your root security certificates on Yosemite expired years ago.
Mozilla formally moved OS X 10.9 (Mavericks), 10.10 (Yosemite), and 10.11 (El Capitan) users to the Extended Support Release (ESR) life cycle. Official support for this specific branch ended on . No further updates or security patches have been issued for this system since that date. Technical Specifications Overview Operating System OS X Yosemite 10.10.5 Last Compatible Build Firefox Extended Support Release (ESR) 78.15.0 Release Date October 5, 2021 Download Package Format DMG Installer Architecture Support Intel 64-bit Processors Step-by-Step Installation Guide firefox download for mac 10105 upd
Firefox Download for Mac 10.10.5 (Yosemite): Safe & Secure Guide
: Firefox 78 ESR stopped receiving security updates in October 2021 . Using it for sensitive activities like online banking is not recommended as it lacks modern protection against newer threats.
Because Firefox 78 ESR reached its final security cycle in October 2021, you must alter the default browser engine properties to maintain functionality and preserve resources on older hardware. Terminate Automated Update Loops Even though Firefox generally runs smoothly on macOS 10
Drops memory overhead by stopping distinct multi-process rendering loops. layers.acceleration.disabled
A window will appear; drag the into your Applications folder.
: Mozilla transitioned Yosemite users to the Extended Support Release (ESR) pipeline to provide security updates for as long as possible. That pipeline officially ended with version 78.15.0esr on October 5, 2021. How to Safely Download Firefox 78.15.0esr for Mac 10.10.5 Mozilla formally moved OS X 10
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If Firefox 78 does not meet your needs, some users on legacy macOS versions look toward community-maintained browsers like Pale Moon or SeaMonkey , though compatibility varies.
: End-of-life. No further security patches or feature updates are provided, leaving the browser vulnerable to modern exploits. Modern Compatibility