Is there a reason you want both? You can install both, but there is no real reason to.

You can find the full version of the current Firefox release (55.0.3) in all languages and all operating systems here: *https://www.mozilla.org/en-US/firefox/all/ *https://www.mozilla.org/en-US/firefox/notes/ It is probably better to use a separate profile for each version, even when these are the same Firefox version because Firefox checks via the compatibility.ini file which Firefox version (file path) last used the profile and resets (initializes) the profile when this doesn't match. See: *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