Development of mobile web-centric OS such as Firefox OS has created new challenges, and opportunities for digital investigators. Network traffic forensic plays an important role in cybercrime investigation to detect subject(s) and object(s) of the crime. In this chapter, we detect and analyze residual network traffic artefacts of Firefox OS in relation to two popular social networking applications (Facebook and Twitter) and one instant messaging application (Telegram). We utilized a Firefox OS simulator to generate relevant traffic while all communication data were captured using network monitoring tools. Captured network packets were examined and remnants with forensic value were reported. This paper as the first focused study on mobile Firefox OS network traffic analysis should pave the way for the future research in this direction.