<!doctype html>
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1663740">
<style>
@namespace url(http://www.w3.org/1998/Math/MathML);
* {
  all: inherit;
  overflow-inline: hidden;
}
</style>
<script>
window.addEventListener('load', () => {
  var x = document.getElementById('a')
  x.setAttribute('mathvariant', 'double-struck')
  x.innerHTML = '<select></select>'
})
</script>
<math id='a'>
