U.S. stock-market indexes opened mostly lower open on Thursday, with outsize losses in the Nasdaq as Facebook shares plummeted following its disappointing quarterly results. Facebook Inc.'s slide appeared to spark broader caution, given the social-media giant is one of the bellwethers of the technology and internet-related sector. The S&P 500 SPX, +0.29% fell 8 points, or 0.3%, to 2,838. The Nasdaq Composite Index COMP, +0.36% slumped 74 points, or, 1%, to 7,857 at the open, driven by a 18% drop in shares of Facebook Inc. FB, +0.20% after disappointing earnings. The Dow Jones Industrial Average DJIA, +0.19% bucked the trend, rising 89 points, or 0.4%, to 25,507.