Ever sent a Facebook friend a greeting through Stories? Facebook is making that much easier to do with a new feature that levels up its birthday reminders and poses a challenge to the greeting card industry. Birthday Stories takes you to an interface where you can easily create a card by adding a photo, a video or a written greeting for the celebrant. The cards will be visible for 24 hours like other Stories, and the recipient will be able to control who can see them -- sort of a like a mixed-media slideshow made especially for them.