diff --git a/etemplate/inc/class.vfs_widget.inc.php b/etemplate/inc/class.vfs_widget.inc.php
index 948c11b609..24b2aa6c7b 100644
--- a/etemplate/inc/class.vfs_widget.inc.php
+++ b/etemplate/inc/class.vfs_widget.inc.php
@@ -337,6 +337,11 @@ class vfs_widget
 					{
 						$thparams['thsize'] = $thsize;
 					}
+					// add modification time to url to allow long caching
+					if (is_array($value) && $value['mtime'])
+					{
+						$thparams['mtime'] = $value['mtime'];
+					}
 
 					$value = $GLOBALS['egw']->link('/etemplate/thumbnail.php', $thparams);
 				}
diff --git a/etemplate/js/et2_widget_vfs.js b/etemplate/js/et2_widget_vfs.js
index 4fafdfc2ba..ddd0a278ad 100644
--- a/etemplate/js/et2_widget_vfs.js
+++ b/etemplate/js/et2_widget_vfs.js
@@ -333,7 +333,7 @@ var et2_vfsMime = expose(et2_valueWidget.extend([et2_IDetachedDOM],
 				title: _value.name,
 				type: _value.mime,
 				poster:'', // TODO: Should be changed by correct video thumbnail later
-				thumbnail:this.egw().mime_icon(_value['mime'], _value['path']) ,
+				thumbnail: this.egw().mime_icon(_value.mime, _value.path, undefined, _value.mtime),
 				href: base_url + _value.download_url
 			}];
 		}
@@ -343,7 +343,7 @@ var et2_vfsMime = expose(et2_valueWidget.extend([et2_IDetachedDOM],
 				title: _value.name,
 				href: base_url + _value.download_url,
 				type: _value.mime,
-				thumbnail: _value.path && _value.mime ? this.egw().mime_icon(_value['mime'], _value['path']) : this.image.attr('src')+ '&thheight=128'
+				thumbnail: _value.path && _value.mime ? this.egw().mime_icon(_value.mime, _value.path, undefined, _value.mtime) : this.image.attr('src')+ '&thheight=128'
 			}];
 		}
 		return mediaContent;
@@ -355,7 +355,7 @@ var et2_vfsMime = expose(et2_valueWidget.extend([et2_IDetachedDOM],
 			this.egw().debug("warn", "%s only has path, needs array with path & mime", this.id, _value);
 			// Keep going, will be 'unknown type'
 		}
-		var src = this.egw().mime_icon(_value['mime'], _value['path']);
+		var src = this.egw().mime_icon(_value.mime, _value.path, undefined, _value.mtime);
 		if(src)
 		{
 			// Set size of thumbnail
diff --git a/etemplate/thumbnail.php b/etemplate/thumbnail.php
index 6ce4dfb845..805b35af78 100644
--- a/etemplate/thumbnail.php
+++ b/etemplate/thumbnail.php
@@ -176,8 +176,8 @@ function read_thumbnail($src)
 		if ($dst)
 		{
 			// Allow client to cache these, makes scrolling in filemanager much nicer
-			header('Pragma: private');
-			header('Cache-Control: max-age=300');
+			// setting maximum allow caching time of one year, if url contains (non-empty) moditication time
+			egw_session::cache_control(empty($_GET['mtime']) ? 300 : 31536000, true);	// true = private / browser only caching
 			header('Content-Type: '.$output_mime);
 			readfile($dst);
 			return true;
@@ -386,6 +386,10 @@ function get_pdf_thumbnail($file)
 {
 	if(!class_exists('Imagick')) return false;
 
+	// switch off max_excution_time, as some thumbnails take longer and
+	// will be startet over and over again, if they dont finish
+	@set_time_limit(0);
+
 	$im = new Imagick($file);
 	$im->setimageformat('png');
 	$im->setresolution(300, 300);
diff --git a/phpgwapi/inc/class.egw_session.inc.php b/phpgwapi/inc/class.egw_session.inc.php
index 76d095a752..2f56a5ea1b 100644
--- a/phpgwapi/inc/class.egw_session.inc.php
+++ b/phpgwapi/inc/class.egw_session.inc.php
@@ -1599,14 +1599,17 @@ class egw_session
 	}
 
 	/**
-	 * Controling caching and expires header, based on $GLOBALS['egw_info']['flags']['nocachecontrol']:
+	 * Controling caching and expires header
+	 *
+	 * Headers are send based on given parameters or $GLOBALS['egw_info']['flags']['nocachecontrol']:
 	 * - not set of false --> no caching (default)
 	 * - true --> private caching by browser (no expires header)
 	 * - "public" or integer --> public caching with given cache_expire in minutes or php.ini default session_cache_expire
 	 *
 	 * @param int $expire =null expiration time in seconds, default $GLOBALS['egw_info']['flags']['nocachecontrol'] or php.ini session.cache_expire
+	 * @param int $private =null allows to set private caching with given expiration time, by setting it to true
 	 */
-	public static function cache_control($expire=null)
+	public static function cache_control($expire=null, $private=null)
 	{
 		if (is_null($expire) && isset($GLOBALS['egw_info']['flags']['nocachecontrol']) && is_int($GLOBALS['egw_info']['flags']['nocachecontrol']))
 		{
@@ -1616,18 +1619,19 @@ class egw_session
 		if (!isset($_SESSION))
 		{
 			// controling caching and expires header
-			if(!isset($GLOBALS['egw_info']['flags']['nocachecontrol']) || !$GLOBALS['egw_info']['flags']['nocachecontrol'])
+			if(!isset($expire) && (!isset($GLOBALS['egw_info']['flags']['nocachecontrol']) ||
+				!$GLOBALS['egw_info']['flags']['nocachecontrol']))
 			{
 				session_cache_limiter('nocache');
 			}
-			elseif ($GLOBALS['egw_info']['flags']['nocachecontrol'] === 'public' || is_int($GLOBALS['egw_info']['flags']['nocachecontrol']))
+			elseif (isset($expire) || $GLOBALS['egw_info']['flags']['nocachecontrol'] === 'public' || is_int($GLOBALS['egw_info']['flags']['nocachecontrol']))
 			{
 				// allow public caching: proxys, cdns, ...
 				if (isset($expire))
 				{
 					session_cache_expire((int)ceil($expire/60));	// in minutes
 				}
-				session_cache_limiter('public');
+				session_cache_limiter($private ? 'private' : 'public');
 			}
 			else
 			{
@@ -1652,6 +1656,11 @@ class egw_session
 					header('Cache-Control: private, max-age='.(60*session_cache_expire()));
 					header_remove('Expires');
 				}
+				elseif ($private)
+				{
+					header('Cache-Control: private, max-age='.$expire);
+					header('Expires: ' . gmdate('D, d M Y H:i:s', time()+$expire) . ' GMT');
+				}
 				else
 				{
 					header('Cache-Control: public, max-age='.$expire);
diff --git a/phpgwapi/js/jsapi/egw_images.js b/phpgwapi/js/jsapi/egw_images.js
index 51f2c2edb6..8b069b0b9a 100644
--- a/phpgwapi/js/jsapi/egw_images.js
+++ b/phpgwapi/js/jsapi/egw_images.js
@@ -119,9 +119,10 @@ egw.extend('images', egw.MODULE_GLOBAL, function() {
 		 * @param {string} _mime
 		 * @param {string} _path vfs path to generate thumbnails for images
 		 * @param {number} _size defaults to 128 (only supported size currently)
+		 * @param {number} _mtime current modification time of file to allow infinit caching as url changes
 		 * @returns url of image
 		 */
-		mime_icon: function(_mime, _path, _size)
+		mime_icon: function(_mime, _path, _size, _mtime)
 		{
 			if (typeof _size == 'undefined') _size = 128;
 			if (!_mime) _mime = 'unknown';
@@ -137,13 +138,14 @@ egw.extend('images', egw.MODULE_GLOBAL, function() {
 			else if (typeof _path == 'string' && (type[0] == 'image' && type[1].match(/^(png|jpe?g|gif|bmp)$/) ||
 				type[0] == 'application' && (type[1].indexOf('vnd.oasis.opendocument.') === 0 || type[1] == 'pdf')))
 			{
-				var thsize = this.config('link_list_thumbnail') || 64;
-				image = this.link('/etemplate/thumbnail.php',{ 'path': _path, 'thsize': thsize});
+				var params = { 'path': _path, 'thsize': this.config('link_list_thumbnail') || 64};
+				if (_mtime) params.mtime = _mtime;
+				image = this.link('/etemplate/thumbnail.php', params);
 			}
 			else
 			{
 				if ((typeof type[1] == 'undefined' || !(image = this.image('mime'+_size+'_'+type[0]+'_'+type[1], 'etemplate')) &&
-					!(typeof mime_alias_map[_mime] != 'undefined' && (image=this.mime_icon(mime_alias_map[_mime], _path, _size)))) &&
+					!(typeof mime_alias_map[_mime] != 'undefined' && (image=this.mime_icon(mime_alias_map[_mime], _path, _size, _mtime)))) &&
 					!(image = this.image('mime'+_size+'_'+type[0], 'etemplate')))
 				{
 					image = this.image('mime'+_size+'_unknown', 'etemplate');