I suggest always using Save when you download a program. That way you can be sure your antivirus software will scan the installer before you run it. Also, in case you need to run it again, you won't have to download it again. Some security software blocks the small "Stub" installer. If you have difficulties getting the Firefox installer to run, you can download the "full" installer from this page (scroll down to your preferred language): https://www.mozilla.org/firefox/all/