JS autocomplete test "clicking on actions should not prevent the menu from ever closing (MBS-6978)" circumstantially fails on assertion "menu is hidden after blurring the autocomplete"

JavaScript tests can be run in two different ways:

• either browsing /static/scripts/tests/all.html:
  then the assertion "menu is hidden after blurring the autocomplete" randomly fails (using Firefox 48.0.2), see attached screenshot,

  # clicking on actions should not prevent the menu from ever closing (MBS-6978)
  ok 3 menu is open after search
  not ok 4 menu is hidden after blurring the autocomplete
    ---
      operator: ok
      expected: true
      actual:   false
    ...
  

• or running prove -l t/js.t:
  then the assertion "menu is hidden after blurring the autocomplete" consistently fails (using Node.js v6.3.1), see attached log file.
  This one can be ignored by moving blurAutocomplete call three lines below.

However, it never fails using Jenkins on https://ci.metabrainz.org/.