The last official Firefox release that officially supports macOS 10.9-10.11 is .
sudo spctl --master-disable
(Change en-US to your language, e.g., de , fr , ja ).
: You can download this specific legacy version directly from the Mozilla FTP Archive. How to Install
If you’re stuck on 10.10.5, either:
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.
Running an older Mac with OS X 10.10.5 Yosemite doesn't mean you have to give up on web browsing. While modern, secure browsers often require newer operating systems, Firefox offers a pathway for older machines to stay functional.
Search for app.update.auto and toggle its boolean value to .
Once the download is complete, installing Firefox is a quick and easy process. Follow these steps:
(Re-enable after install: sudo spctl --master-enable )