Do a custom install and install each version in its own program folder to use multiple Firefox versions. * https://support.mozilla.com/kb/Custom+installation+of+Firefox+on+Windows * https://support.mozilla.org/kb/Installing+a+previous+version+of+Firefox Create a new profile exclusively for each Firefox version.<br /> Create a desktop shortcut with -P "profile" appended to the target to launch each Firefox version with its own profile. * 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