Firefox 116.0 and later including Firefox 135.0.1 and 128.7,2 requires Windows 10, 11 to run. Firefox 115 ESR currently at 115.20.0esr is the most current version you can run on the eol Windows 7, 8, 8.1. https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support Besides update to Windows 10 or 11 the other option is to perhaps dual boot with a Linux distro to have current versions of Firefox. I do suggest using a lighter desktop like Xfce or Mate over the heavier Gnome and KDE.