Intermittent failure in /_mozilla/mozilla/hit_test_pos_fixed.html

[jdm]

  ▶ Unexpected subtest result in /_mozilla/mozilla/hit_test_pos_fixed.html:
  │ FAIL [expected PASS] Hit-test of an element with position: fixed should discard scroll offset
  │   → assert_true: should be able to hit the fixed-positioned element expected true got false
  │ 
  │ window.onload<@http://web-platform.test:8000/_mozilla/mozilla/hit_test_pos_fixed.html:37:5
  │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:1538:20
  └ Test.prototype.step_func/<@http://web-platform.test:8000/resources/testharness.js:1562:20