Used to check all checkboxes in a page.

check_all.js

// Paste into Firebug or Chrome Dev Tools console
// when viewing a page with multiple checkboxes.

(function(d) {
  var input = d.querySelectorAll('input[type="checkbox"]');
  var i = input.length;

  while (i--) {
    input[i].checked = true;
  }
})(this.document);

Thanks! @nathansmith