Shares of Netflix fell 5.8% today as the king of online movie rentals took some hits from multiple sides during the past 24 hours — a significant dent in the fender for a company whose stock more than tripled last year. Earlier in the day, Warner Bros. announced that it is using Facebook to offer pay-per-view movies for 48 hours in exchange for 30 Facebook Credits ($3) to its network of more than 500 million users. Selected movies will be offered on each film’s Facebook page, starting today with The Dark Knight. The move comes on the heels of initiatives from such players as Time Warner (HBO Go), which seek to find their own way against Netflix. As another recent example, Comcast cable president Neil Smit said Monday during a Deutsche Bank investors conference in Florida that he his confident his company can compete in the sector via video-on-demand offerings and new content, compared with Netflix’s emphasis on library titles.