According to your More System details on right of your post, it appears you are running Firefox 78 on the old macOS 10.10. Firefox 79.0 to 115 ESR requires macOS 10.12, 10.13, 10.14 ro run while Firefox 116.0 to current requires macOS 10.15 (ten.fifteen) or later to run. Since you appear to be running macOS 10.10 the latest version you can run is Fx 78.15.0esr which you may already have. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr Unless your hardware allows for a macOS update to 10.12 (ten.twelve) or later in order to use Firefox 115 ESR, you are stuck with Firefox 78.15.0esr.