"border" attribute is not a valid attribute for <img /> tags. Using proper CSS instructions instead.

css/default.css

@@ -2,6 +2,10 @@ body {background-color: #F9F9F9;}
 body.error {background-color: #F0F0F0;}
 body,th,td,ul,li,a,div,p,pre {color:#333333; font-family:Verdana,"Bitstream Vera Sans",Arial,Helvetica,Sans,"Bitstream Vera Serif"; font-size:9.0pt;}
 
+a img {
+  border:none;
+}
+
 h1 {
   margin-bottom:1.5em;
 }
@@ -78,6 +82,10 @@ a#owncloud-logo span {
   text-decoration:none;
 }
 
+.navigationitem1 img {
+  border:none;
+}
+
 .navigationitem1:hover {
   background-color: #EEEEEE;
 }

inc/lib_base.php

@@ -133,7 +133,7 @@ class OC_UTIL {
    */
   public static function shownavigation(){
     echo('<table cellpadding="5" cellspacing="0" border="0"><tr>');
-    echo('<td class="navigationitem1"><a href="/">'.$_SESSION['username'].'</a> <img src="/img/dots.png" border="0"></td>');
+    echo('<td class="navigationitem1"><a href="/">'.$_SESSION['username'].'</a> <img src="/img/dots.png" /></td>');
     if($_SERVER['SCRIPT_NAME']=='/index.php') echo('<td class="navigationitemselected"><a href="/">Files</a></td>'); else echo('<td class="navigationitem"><a href="/">Files</a></td>');
 
     foreach(OC_UTIL::$NAVIGATION as $NAVI) {

inc/lib_files.php

@@ -53,7 +53,7 @@ class OC_FILES {
       $currentdir='';
       foreach($dirs as $d) {
         $currentdir.='/'.$d.'';
-        if($d<>'') echo('<td class="nametext"><a href="/?dir='.$currentdir.'"><img src="/img/arrow.png" border="0" />&nbsp;'.$d.'</a></td>');
+        if($d<>'') echo('<td class="nametext"><a href="/?dir='.$currentdir.'"><img src="/img/arrow.png" />&nbsp;'.$d.'</a></td>');
       }
       echo('</tr></table></div>');
     }