The Useragent you used to post this thread appears to be on macOS 10.11 Mozilla/5.0 (Macintosh; Intel '''Mac OS X 10.11'''; rv:78.0) Gecko/20100101 Firefox/78.0 For macOS 10.9, 10.10, 10.11 users the Fx 78.15.0esr is the last to still support. For macOS 10.12, 10.13, 10.14 the most current you can use is 115.0 ESR as Fx 116.0 and later requires macOS 10.15 (ten fifteen) or later. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support However for your macOS 10.15 system you can download the current Firefox 126.0.1 Release from https://www.mozilla.org/firefox/all/#product-desktop-release Fx 115.0 ESR from https://www.mozilla.org/firefox/all/#product-desktop-esr