value property of a
<select> element to a value that matched no
<option> did not update the selection accordingly, when the
<select> element was displayed as a combobox.
Firefox 46 has fixed this bug as per the HTML spec so that any
<option> will be unselected in such cases. That means the
value properties of the
<select> element will become
-1, an empty
HTMLCollection and an empty string respectively.
While the new behaviour should match other browsers, certain sites with Firefox-specific code could be broken with this change.