On the verge of tears, Nathan Nkunzimana recalled watching a video of a child being molested and another of a woman being killed. Eight hours a day, his job as a content moderator for a Facebook contractor required him to look at horrors so the world wouldn’t have to. Some overwhelmed colleagues would scream or cry, he said. Now, Nkunzimana is among nearly 200 former employees in Kenya who are suing Facebook and local contractor Sama over working conditions that could have implications for social media moderators around the world. It is the first known court challenge outside the United...