Firts, Highslide effect is integrated to the SmartResizer pluging and should work on Joomla 3.0
Second, Unfortunately this is a known issue of Joomla SqweezBox effect. You can try to adapt image size parameters to remove scrollbars in source code in this line:
$text = '<a style="background:none;" rel="{handler: \'iframe\', size: {x: '.$image_width.', y: '.$image_height.'}}" target="_blank" href="'.$src.'" onclick="SqueezeBox.fromElement(this,{parse: \'rel\'});return false;" >'.$text.'</a>';
