You can install the Firefox 17 ESR version alongside of your current Firefox 24 ESR version via a custom install. * https://support.mozilla.com/kb/Custom+installation+of+Firefox+on+Windows *http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/17.0.11esr/ Make sure to use a separate profile for each version. Use the Profile Manager to create a new profile for this version, so make sure not to start Firefox after the installation has finished. Create a desktop shortcut with -P "profile" appended to the target to launch each Firefox version with its own profile. *https://support.mozilla.org/kb/Managing+profiles *http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows *http://kb.mozillazine.org/Shortcut_to_a_specific_profile *http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox *https://developer.mozilla.org/Mozilla/Multiple_Firefox_Profiles ---- You can also 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 the currently installed release version. *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://sourceforge.net/projects/osxportableapps/files/Portable%20Firefox%20OS%20X/ *http://portableapps.com/support/firefox_portable#helper_apps