Why does the call to focus() not work here?

Sorry, Javasvript noob here…

In the code below, why does the focus not go (back) to the text field “id1” when I enter an illegal value (= anything other than 1 to 9) in that field? The problem seems to be FF-specific. It works as I’d expect in Chromium. Any ideas on how to get it to work in FF?

<!DOCTYPE html>
<input type="text" id="id1">
<input type="text" id="id2">
document.getElementById("id1").addEventListener("change", function() { single_digit("id1"); } );

function single_digit(item)
  f = document.getElementById(item);

  if (!/^[1-9]$/.test(f.value)) {
    f.value = '';

Thanks for any insights/help/tips/words of comfort you may be able to provide!

Found a solution: https://coderanch.com/t/464594/languages/focus-working-firefox