To view all versions...
https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/
To install 31.0esr
https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/31.0esr/
Click on Win32
https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/31.0esr/win32/
Click on en-US
https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/31.0esr/win32/en-US/
Click on
Firefox Setup 31.0esr.exe
Now you can install Mozilla Firefox 31.0esr
