: Some modern websites may not load correctly due to expired root certificates on older macOS versions. Install firefox for Mac IOS 10.11.6 - Mozilla Support
The most current and compatible version of Firefox for is Firefox 78.15.0 ESR (Extended Support Release) . Later versions, including Firefox 79 and beyond, require a minimum of macOS 10.12 (Sierra). How to Download Firefox for Mac 10.11.6 how to download firefox for mac 10.11.6
: A window will pop up showing the Firefox icon. Drag the Firefox icon into the Applications folder icon in that same window. : Some modern websites may not load correctly