check_all.js

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

(function(d) {
  var input = d.getElementsByTagName('input');
  var i = input.length;

  while (i--) {
    if (input[i].type === 'checkbox') {
      input[i].setAttribute('checked', 'checked');
    }
  }
})(this.document);