For users still running macOS 10.10.5 (Yosemite), the final supported version of Firefox is Firefox 78.15.0 ESR (Extended Support Release).
Why this version? It was the last major release to officially support Yosemite. firefox download for mac 10105 upd
| Firefox Version | macOS 10.10.5 | Security Updates | |----------------|---------------|------------------| | Firefox 78 ESR | ✅ Yes | ❌ No (EOL) | | Firefox 79+ | ❌ No | N/A | For users still running macOS 10
Or download from Mozilla’s official “Firefox for older Macs” page: firefox download for mac 10105 upd
Steps: