From https://bugzilla.mozilla.org/show_bug.cgi?id=1372325#c14

Sample is the following.

var utter = new SpeechSynthesisUtterance("Hello World");
utter.onend = () => {
  // Edge, WebKit and Blink allow this, but Firefox doesn't.
  window.speechSynthesis.speak(utter);
};
window.speechSynthesis.speak(utter);

Google search page uses that SpeechSynthesisUtterance is reused. But Speech API doesn't define whether this object is reusable.

Edge, WebKit, and Blink allow SpeechSynthesisUtterance is reusable now, but Gecko doesn't. If it allow to reuse this object, we should add spec/document about reusable.