https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support With the EOL Windows 7, 8, 8.1 the most current Firefox you can run is Firefox 115 ESR currently at Fx 115.34.0esr. Firefox 116.0 and later including the Fx 149.0 release and 140.9.0esr requires Windows 10, 11 to run. To download the current Firefox 115 SER for Windows https://www.firefox.com/download/all/desktop-esr/ > Pick 64-bit or 32-bit Windows > Language you want > then click on { Download ESR 115 } to download the full offline Firefox 115.34.0esr setup .exe.