[CSSTransition-effect.tentative.html]
  [After setting a transition's effect to null, a new transition can be started]
    expected:
      if (os == "linux") and debug and webrender and fission: ["FAIL", "PASS"]
      if (os == "linux") and debug and not webrender: ["FAIL", "PASS"]
      if (os == "linux") and not debug: ["FAIL", "PASS"]
      if os == "mac": ["FAIL", "PASS"]
      FAIL