No need to use window.parent to reference metaslider_slider_id

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@909713 b8457f37-d9ea-0310-8a92-e5e31aec5664
Stop firefox highlighting selected thumbnails

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@909715 b8457f37-d9ea-0310-8a92-e5e31aec5664