download firefox / thunderbird extended support release (esr)
Mozilla Firefox ESR is meant for organizations that manage their client desktops, including schools, businesses and other instituitions that want to offer Firefox.

http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/latest-esr/win32/en-GB/
http://download.cdn.mozilla.net/pub/mozilla.org/thunderbird/releases/latest-esr/win32/en-GB/