The steps to putting a Facebook video on your computer are a bit convoluted, but not difficult. If the owner deletes the video, you won't have access to it anymore. But that's not for saving the video to your local storage-it only 'saves' it on Facebook to a section of your account called 'Saved Videos,' where you can create collections to watch later. Facebook provides a 'Save Video' link in the ellipsis menu next to almost every video.
