https://support.mozilla.org/en-US/kb/install-older-version-of-firefox?cache=no Be sure to read everything here. If you still want to downgrade, look under; '''I still want to downgrade. ''' Click the '''Directory of other versions and languages''' link. Look for the directory of the version that you want. But, remember that '''old versions may have security issues. ''' You should also check out Firefox; Extended Support Release https://www.mozilla.org/en-US/firefox/organizations/ https://www.mozilla.org/en-US/firefox/organizations/notes/ https://www.mozilla.org/en-US/firefox/organizations/system-requirements/

You can install a portable (ESR) Firefox version to access websites that do not work with the current Firefox release. The portable version comes with its own profile folder and doesn't interfere with currently installed Firefox versions. *http://portableapps.com/apps/internet/firefox_portable *http://portableapps.com/apps/internet/firefox-portable-esr *http://sourceforge.net/projects/portableapps/files/Mozilla%20Firefox%2C%20Portable%20Ed./ *http://www.freesmug.org/portableapps:firefox#toc1 *http://portableapps.com/support/firefox_portable#helper_apps