[before-prepare-iframe-success-external-classic.html]
  [<script> error: Move success external classic script to iframe before-prepare]
    disabled:
      if tsan: https://bugzilla.mozilla.org/show_bug.cgi?id=1722918
    expected:
      if (os == "linux") and debug and not fission: [PASS, FAIL]
      if (os == "mac") and not debug: [PASS, FAIL]
      if (os == "mac") and debug: [PASS, FAIL]
