There is not a way to save a direct link on the Home page of a Fire Tablet (although you can the Facebook app icon to your Home screen by pressing, holding and dragging the icon). Have you tried using the Silk Browser to access your Facebook Selling sites, and saving it as a Bookmark?
To bookmark a webpage, tap the bookmark icon in the URL bar near the top of the screen.
To view or manage your bookmarks, open Silk and swipe from the left side of the screen, and then tap Bookmarks. You’ll see a new screen showing all of your bookmarks. Press and hold any bookmarked site to see more options.