Some heavily-shorted consumer Internet stocks are closing out the week on a high note. FB +3.4%. ZNGA +8.3%. YELP +6.1%. GRPN +1.9%. Goldman's Heather Bellini is talking up the potential of Facebook's Gifts product, which it began heavily promoting during the holiday season. Assuming Facebook gets a 12% cut on sales, Bellini thinks Gifts could deliver $75M-$110M in 2013 revenue in the event 5% of U.S. users buy an average of 5 gifts over the course of the year.