Project https://github.com/Eclipse-Community/r3dfox as FF clone works on Win 7!
Latest offline installer of FF is at https://download-installer.cdn.mozilla.net/pub/firefox/releases/126.0/win64/en-GB/
Since version 125, VxKex can not run FF on Win 7.
Unpacked FF 126.0 x86/x64 works on Win 7 by borrowing libs from r3dfox project of the same version. Libs are:
lgpllibs.dll
xul.dll
nssckbi.dll (new problem for LibreWolf + about:config does not work)
Firefox.exe, private-browsing.exe are runnable on Windows Vista+.
Force closing after 1-2 minutes is fixed. WebGL is enabled.