Well you could download the current Firefox 116 ESR which is currently at 115.30.0esr on a another computer and then transfer over to the Win7 system with a usb flash drive. https://www.firefox.com/download/all/desktop-esr/ then pick the 64-bit or 32-bit Windows, then language then click on the {Download ESR 115] to get Fx 115.30.0esr as the download now will serve you Fx 140.5.0esr that will not run. https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support