The release of version 66.0.5 was a response to an expired intermediate certificate that caused Firefox to incorrectly flag nearly all add-ons as "unsupported," disabling them instantly.
For the standard US English version, navigate to the win64/en-US (for 64-bit Windows) or mac/en-US (for macOS) folders within the archive. download firefox 66.0.5
Downloading version 66.0.5 grants access to all the core features of the 66 series: Firefox 66.0.5, See All New Features, Updates and Fixes The release of version 66
If you need this specific legacy version for compatibility or testing, it is available through official Mozilla channels: Why Firefox 66
Mobile users can find the corresponding release in the Android release notes archive . Why Firefox 66.0.5 Was Essential
You can find the full directory of installation files for Windows, Mac, and Linux on the Mozilla FTP Server .
Firefox 66.0.5 was a critical stability update released on May 7, 2019, primarily to resolve a widespread issue where browser extensions and themes were being disabled. This version serves as the final refinement for the Firefox 66 branch, ensuring that users can maintain their customized browsing experience without interruption.