Large empty space under the widget

Hi! You should turn off the “Show expanded when Javascript disabled” option, because you have a code in this file:
https://wp2.wilmaweb.de/wp-content/themes/twentythirteen/js/functions.js
That if the sidebar widget has a bigger height, than the rest of the page, this will put that extra margin there which it needs to keep the footer visible:

/**
	 * Adds a top margin to the footer if the sidebar widget area is higher
	 * than the rest of the page, to help the footer always visually clear
	 * the sidebar.
	 */
	$( function() {
		if ( body.is( '.sidebar' ) ) {
			var sidebar   = $( '#secondary .widget-area' ),
			    secondary = ( 0 === sidebar.length ) ? -40 : sidebar.height(),
			    margin    = $( '#tertiary .widget-area' ).height() - $( '#content' ).height() - secondary;

			if ( margin > 0 && _window.innerWidth() > 999 ) {
				$( '#colophon' ).css( 'margin-top', margin + 'px' );
			}
		}
	} );

So our menu is actually loading completely opened because of this javascript disabled option, and our javascript code is closing it up, but your theme’s code runs sooner, than ours, which makes the calculation using the completely opened menu’s height.

Thank you very much for the super quick help! The solution is so simple and logical :))

Your plugin is really great. I’ll try to convince my website client to buy the Pro version.