diff --git a/mozilla/mail/base/content/commandglue.js b/mozilla/mail/base/content/commandglue.js
index d939dc50a83..d106a62481c 100644
--- a/mozilla/mail/base/content/commandglue.js
+++ b/mozilla/mail/base/content/commandglue.js
@@ -820,6 +820,7 @@ function FolderPaneSelectionChange()
         }
         else
         {
+            OnLeavingFolder(gPrevSelectedFolder);  // mark all read in last folder
             var sortType = 0;
             var sortOrder = 0;
             var viewFlags = 0;
@@ -1149,6 +1150,19 @@ function CreateGroupedSearchTerms(searchTermsArray)
   return searchTermsArrayForQS;
 }
 
+function OnLeavingFolder(aFolder)
+{
+  try
+  {
+    if (gPrefBranch.getBoolPref("mailnews.mark_message_read." + aFolder.server.type))
+    {
+      // mark all messages of aFolder as read
+      goDoCommand('cmd_markAllRead');
+    }
+  }
+  catch(e){/* ignore */}
+}
+
 var gViewDebug = false;
 
 function viewDebug(str)
diff --git a/mozilla/mail/base/content/msgMail3PaneWindow.js b/mozilla/mail/base/content/msgMail3PaneWindow.js
index 216e6ff3119..119b75a7887 100644
--- a/mozilla/mail/base/content/msgMail3PaneWindow.js
+++ b/mozilla/mail/base/content/msgMail3PaneWindow.js
@@ -827,6 +827,7 @@ function delayedOnLoadMessenger()
 
 function OnUnloadMessenger()
 {
+  OnLeavingFolder(gMsgFolderSelected);  // mark all read in current folder
   accountManager.removeIncomingServerListener(gThreePaneIncomingServerListener);
   pref.QueryInterface(Components.interfaces.nsIPrefBranchInternal);
   pref.removeObserver("mail.pane_config.dynamic", MailPrefObserver);
diff --git a/mozilla/mailnews/base/resources/content/commandglue.js b/mozilla/mailnews/base/resources/content/commandglue.js
index c2fa8d88e93..042afae5474 100644
--- a/mozilla/mailnews/base/resources/content/commandglue.js
+++ b/mozilla/mailnews/base/resources/content/commandglue.js
@@ -838,6 +838,7 @@ function FolderPaneSelectionChange()
         }
         else
         {
+            OnLeavingFolder(gPrevSelectedFolder);  // mark all read in last folder
             var sortType = 0;
             var sortOrder = 0;
             var viewFlags = 0;
@@ -1188,6 +1189,19 @@ function CreateGroupedSearchTerms(searchTermsArray)
   return searchTermsArrayForQS;
 }
 
+function OnLeavingFolder(aFolder)
+{
+  try
+  {
+    if (gPrefBranch.getBoolPref("mailnews.mark_message_read." + aFolder.server.type))
+    {
+      // mark all messages of aFolder as read
+      goDoCommand('cmd_markAllRead');
+    }
+  }
+  catch(e){/* ignore */}
+}
+
 var gViewDebug = false;
 
 function viewDebug(str)
diff --git a/mozilla/mailnews/base/resources/content/msgMail3PaneWindow.js b/mozilla/mailnews/base/resources/content/msgMail3PaneWindow.js
index c378016493e..b9d8d35a363 100644
--- a/mozilla/mailnews/base/resources/content/msgMail3PaneWindow.js
+++ b/mozilla/mailnews/base/resources/content/msgMail3PaneWindow.js
@@ -745,6 +745,7 @@ function OnUnloadMessenger()
 {
   pref.removeObserver("mail.pane_config.dynamic", MailPaneConfigObserver, false);
 
+  OnLeavingFolder(gMsgFolderSelected);  // mark all read in current folder
   accountManager.removeIncomingServerListener(gThreePaneIncomingServerListener);
   RemoveToolBarPrefListener();
   // FIX ME - later we will be able to use onload from the overlay