prototype/javascript - firefox没有触发keypress/keydown事件,除非焦点在文本框中

document.addEventListener('keydown', function(event) {
  console.log('Key down:', event.keyCode);
});

document.addEventListener('keypress', function(event) {
  console.log('Key press:', event.keyCode);
});

document.observe('keydown', function(event) {
  console.log('Key down:', event.keyCode);
});

document.observe('keypress', function(event) {
  console.log('Key press:', event.keyCode);
});

document.addEventListener('keyup', function(event) {
  console.log('Key up:', event.keyCode);
});