FF scrolls page instead of modal content when pressing cursor keys and PGUP, PGDWN

[samdark]

If content of the modal is clicked once, it works fine.

[samdark]

Got that from Alexey Matveed via email. Not verified:

if (!localOptions.cloning) {
    overlay.data(pluginNamespace+'.el', el);
    $(el).data(pluginNamespace+'.parent', $(el).parent());
    openedModalElement = $(el).appendTo(overlay).prepend($('<a data-focus>').attr('tabindex', "-1")).show();
} else {
    openedModalElement = $(el).clone(true).appendTo(overlay).prepend($('<a data-focus>').attr('tabindex', "-1")).show();
}
overlay.find('[data-focus]').focus();