JavaScript keypress Enter is fired for Japanese IME on FireFox, but not on Edge

I have tried the W3 Schools example code for handling the enter key for input text. I copied the source code from that site's page and pasted below.

The problem is that on FireFox, if I press the enter key to finish Japanese input mode, the code is also triggered. On Edge, it did not. Is this a FireFox bug, or just a different behaviour? Anyway, how can I circumvent this?

var input = document.getElementById("myInput");

// Execute a function when the user presses a key on the keyboard
input.addEventListener("keypress", function(event) {
  // If the user presses the "Enter" key on the keyboard
  if (event.key === "Enter") {
    // Cancel the default action, if needed
    event.preventDefault();
    // Trigger the button element with a click
    document.getElementById("myBtn").click();
  }
});

You should rather use KeyDown event. KeyPress is reporting every keycode from keyboard. Some keys on keyboard are not only putting one keycode but multiple keycodes. KeyDown event should pack all keycode from one actual pressed key into one event.

KeyPress is meant to do more low level approach