You don't say which OS version you have. See the link at the bottom of this support article. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

''<p>android84 [[#question-1387657|said]]</p>'' <blockquote>Downloaded newer version of firefox, but it isn't supported by my current OS. Need to download my older version of firefox so I can still use firefox. </blockquote> Would be helpful if you mentioned what OS/version. Based on your useragent in More system details, it appears you have the old EOL macOS 10.'''11''' Firefox 79.0 and later requires macOS 10.'''12''' at minimum to run. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr The old EOL Firefox 78.15.0 ESR is the most current you can run on macOS 10.9 to 10.11 https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/en-US/ other locales are at https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/