A mortar shell landed in this market in Tripoli, Libya, last week. A parallel battle was heating up on Facebook. CAIRO — When a new bout of fighting between rival militias engulfed the Libyan capital in recent days, badly shaking the fragile United Nations-backed government, some combatants picked up rifles and rocket launchers and headed into the streets. Others logged on to Facebook. As rockets rained on parts of Tripoli, hitting a hotel popular with foreigners and forcing the airport to close, and 400 prisoners escaped from a jail, a parallel battle unfolded online. On their Facebook pages, rival groups issued boasts, taunts and chilling threats — one vowing to “purify” Libya of its opponents. Some “keyboard warriors,” as Facebook partisans are known in Libya, posted fake news or hateful comments. Others offered battlefield guidance. On one discussion page on Thursday, a user posted maps and coordinates to help […]