How to avoid the need for ctrl-click in a multi-select box using Javascript?

Check this fiddle: http://jsfiddle.net/xQqbR/1022/

You basically need to override the mousedown event for each <option> and toggle the selected property there.

$('option').mousedown(function(e) {
    e.preventDefault();
    $(this).prop('selected', !$(this).prop('selected'));
    return false;
});

For simplicity, I’ve given ‘option’ as the selector above. You can fine tune it to match <option>s under specific <select> element(s). For ex: $('#mymultiselect option')