A former police officer has filed a lawsuit against the North Plainfield Police Department, claiming he was fired after seeking treatment for an addiction to medication he was prescribed after a work injury. Francis Steinhauser, 35, states in court papers he admitted himself on July 6, 2020, to an in-patient rehabilitation program at Shatterproof in Florida, which treats first-responders for mental health disorders and substance abuse. “I was injured on the job, had to have two surgeries six months apart,” Steinhauser said in an interview Friday. “I became addicted to the medication and sought…