Even if Matthew McConaughey doesn’t win a lead actor Emmy for his role on HBO’s “True Detective,” there may be consolation. He might be asked to accept — then shake — a comically oversized tablet computer emblazoned with Facebook’s logo. The device, developed by Facebook FB 0.00% and a marketing company, is called the “Mentions Box,” and it’s designed to connect fans on Facebook with their favorite celebrities. Facebook plans to deploy it ...