diff --git a/mail/base/content/mail3PaneWindowCommands.js b/mail/base/content/mail3PaneWindowCommands.js
index 599d4402a89..319bf038ee2 100644
--- a/mail/base/content/mail3PaneWindowCommands.js
+++ b/mail/base/content/mail3PaneWindowCommands.js
@@ -206,7 +206,6 @@ var DefaultController =
 			case "cmd_file":
 			case "cmd_emptyTrash":
 			case "cmd_compactFolder":
-			case "cmd_sortByThread":
   	  case "cmd_settingsOffline":
       case "cmd_close":
       case "cmd_selectAll":
@@ -369,7 +368,6 @@ var DefaultController =
       case "cmd_previousFlaggedMsg":
         return IsViewNavigationItemEnabled();
       case "cmd_viewAllMsgs":
-      case "cmd_sortByThread":
       case "cmd_viewUnreadMsgs":
       case "cmd_viewThreadsWithUnread":
       case "cmd_viewWatchedThreadsWithUnread":
@@ -515,9 +513,6 @@ var DefaultController =
 			case "cmd_previousFlaggedMsg":
 				MsgPreviousFlaggedMessage();
 				break;
-			case "cmd_sortByThread":
-				MsgSortByThread();
-				break;
 			case "cmd_viewAllMsgs":
       case "cmd_viewThreadsWithUnread":
       case "cmd_viewWatchedThreadsWithUnread":
diff --git a/mail/base/content/mailWindowOverlay.js b/mail/base/content/mailWindowOverlay.js
index 5eddd9ecdcb..82a0264ef30 100644
--- a/mail/base/content/mailWindowOverlay.js
+++ b/mail/base/content/mailWindowOverlay.js
@@ -236,7 +236,6 @@ function InitViewSortByMenu()
     setSortByMenuItemCheckState("sortBySizeMenuitem", (sortType == nsMsgViewSortType.bySize));
     setSortByMenuItemCheckState("sortByStatusMenuitem", (sortType == nsMsgViewSortType.byStatus));
     setSortByMenuItemCheckState("sortBySubjectMenuitem", (sortType == nsMsgViewSortType.bySubject));
-    setSortByMenuItemCheckState("sortByThreadMenuitem", (sortType == nsMsgViewSortType.byThread));
     setSortByMenuItemCheckState("sortByUnreadMenuitem", (sortType == nsMsgViewSortType.byUnread));
     setSortByMenuItemCheckState("sortByLabelMenuitem", (sortType == nsMsgViewSortType.byLabel));
     setSortByMenuItemCheckState("sortByJunkStatusMenuitem", (sortType == nsMsgViewSortType.byJunkStatus));
@@ -249,8 +248,15 @@ function InitViewSortByMenu()
     setSortByMenuItemCheckState("sortAscending", (sortOrder == nsMsgViewSortOrder.ascending));
     setSortByMenuItemCheckState("sortDescending", (sortOrder == nsMsgViewSortOrder.descending));
 
-    var threadMenuItem = document.getElementById("sortByThreadMenuitem");
-    threadMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
+    var threaded = ((gDBView.viewFlags & nsMsgViewFlagsType.kThreadedDisplay) != 0);
+    var sortThreadedMenuItem = document.getElementById("sortThreaded");
+    var sortUnthreadedMenuItem = document.getElementById("sortUnthreaded");
+
+    sortThreadedMenuItem.setAttribute("checked", threaded);
+    sortUnthreadedMenuItem.setAttribute("checked", !threaded);
+
+    sortThreadedMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
+    sortUnthreadedMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
 }
 
 function InitViewMessagesMenu()
@@ -281,13 +287,7 @@ function InitViewMessagesMenu()
 
 function InitViewMessageViewMenu()
 {
-  var viewFlags = (gDBView) ? gDBView.viewFlags : 0;
   var viewType = (gDBView) ? gDBView.viewType : 0;
-
-  var threadedMenuItem = document.getElementById("viewThreaded");
-  if (threadedMenuItem)
-    threadedMenuItem.setAttribute("checked", (viewFlags & nsMsgViewFlagsType.kThreadedDisplay) != 0);
-
   var currentViewValue = document.getElementById("viewPicker").value;
 
   var allMenuItem = document.getElementById("viewAll");
diff --git a/mail/base/content/mailWindowOverlay.xul b/mail/base/content/mailWindowOverlay.xul
index 1064a89a165..c8ffb152a35 100644
--- a/mail/base/content/mailWindowOverlay.xul
+++ b/mail/base/content/mailWindowOverlay.xul
@@ -115,7 +115,6 @@
    <command id="cmd_viewThreadsWithUnread" oncommand="goDoCommand('cmd_viewThreadsWithUnread')" disabled="true"/>
    <command id="cmd_viewWatchedThreadsWithUnread" oncommand="goDoCommand('cmd_viewWatchedThreadsWithUnread')" disabled="true"/>
    <command id="cmd_viewIgnoredThreads" oncommand="goDoCommand('cmd_viewIgnoredThreads')" disabled="true"/>
-   <command id="cmd_sortByThread" oncommand="goDoCommand('cmd_sortByThread')" disabled="true"/>
    <commandset id="viewZoomCommands">
      <command id="cmd_textZoomReduce" oncommand="ZoomManager.prototype.getInstance().reduce();"/>
      <command id="cmd_textZoomEnlarge" oncommand="ZoomManager.prototype.getInstance().enlarge();"/>
@@ -1160,7 +1159,6 @@
               <menuitem id="sortBySizeMenuitem" type="radio" name="sortby" label="&sortBySizeCmd.label;" accesskey="&sortBySizeCmd.accesskey;" oncommand="MsgSortBySize()"/>
               <menuitem id="sortByStatusMenuitem" type="radio" name="sortby" label="&sortByStatusCmd.label;" accesskey="&sortByStatusCmd.accesskey;" oncommand="MsgSortByStatus()"/>
               <menuitem id="sortBySubjectMenuitem" type="radio" name="sortby" label="&sortBySubjectCmd.label;" accesskey="&sortBySubjectCmd.accesskey;" oncommand="MsgSortBySubject()"/>
-              <menuitem id="sortByThreadMenuitem" type="radio" name="sortby" label="&sortByThreadCmd.label;"  accesskey="&sortByThreadCmd.accesskey;" oncommand="MsgSortByThread()"/>
               <menuitem id="sortByUnreadMenuitem" type="radio" name="sortby" label="&sortByUnreadCmd.label;"  accesskey="&sortByUnreadCmd.accesskey;" oncommand="MsgSortByUnread()"/>
               <menuitem id="sortByLabelMenuitem" type="radio" name="sortby" label="&sortByLabelCmd.label;" accesskey="&sortByLabelCmd.accesskey;" oncommand="MsgSortByLabel()"/>
               <menuitem id="sortByJunkStatusMenuitem" type="radio" name="sortby" label="&sortByJunkStatusCmd.label;" accesskey="&sortByJunkStatusCmd.accesskey;" oncommand="MsgSortByJunkStatus()"/>
@@ -1168,13 +1166,14 @@
               <menuseparator/>
               <menuitem id="sortAscending" type="radio" name="sortdirection" label="&sortAscending.label;" accesskey="&sortAscending.accesskey;" oncommand="MsgSortAscending()"/>
               <menuitem id="sortDescending" type="radio" name="sortdirection" label="&sortDescending.label;" accesskey="&sortDescending.accesskey;" oncommand="MsgSortDescending()"/>
+              <menuseparator/>
+              <menuitem id="sortThreaded" type="radio" name="threaded" label="&sortThreaded.label;" accesskey="&sortThreaded.accesskey;" oncommand="MsgSortThreaded();"/>
+              <menuitem id="sortUnthreaded" type="radio" name="threaded" label="&sortUnthreaded.label;" accesskey="&sortUnthreaded.accesskey;" oncommand="MsgSortUnthreaded();"/>
             </menupopup>
           </menu>
 
           <menu label="&msgsMenu.label;" id="viewMessageViewMenu" accesskey="&msgsMenu.accesskey;">
             <menupopup id="viewMessageViewPopup" onpopupshowing="InitViewMessageViewMenu()">
-              <menuitem id="viewThreaded" type="checkbox" label="&viewThreaded.label;" accesskey="&viewThreaded.accesskey;" oncommand="MsgToggleThreaded();"/>
-              <menuseparator/>
               <menuitem id="viewAll" type="radio" name="viewmessages" label="&viewAll.label;" accesskey="&viewAll.accesskey;" oncommand="ViewMessagesBy('viewPickerAll');"/>
               <menuitem id="viewUnread" type="radio" name="viewmessages" label="&viewUnread.label;" accesskey="&viewUnread.accesskey;" oncommand="ViewMessagesBy('viewPickerUnread');"/>
               <menuseparator/>
diff --git a/mail/base/locale/messenger.dtd b/mail/base/locale/messenger.dtd
index 30c7f380727..04e7382c67e 100644
--- a/mail/base/locale/messenger.dtd
+++ b/mail/base/locale/messenger.dtd
@@ -147,18 +147,18 @@
 <!ENTITY sortByRecipientCmd.accesskey "c">
 <!ENTITY sortByUnreadCmd.label "Read">
 <!ENTITY sortByUnreadCmd.accesskey "R">
-<!ENTITY sortByThreadCmd.label "Thread">
-<!ENTITY sortByThreadCmd.accesskey "T">
 <!ENTITY sortByOrderReceivedCmd.label "Order Received">
 <!ENTITY sortByOrderReceivedCmd.accesskey "O">
 <!ENTITY sortAscending.label "Ascending">
 <!ENTITY sortAscending.accesskey "A">
 <!ENTITY sortDescending.label "Descending">
 <!ENTITY sortDescending.accesskey "D">
+<!ENTITY sortThreaded.label "Threaded">
+<!ENTITY sortThreaded.accesskey "T">
+<!ENTITY sortUnthreaded.label "Unthreaded">
+<!ENTITY sortUnthreaded.accesskey "h">
 <!ENTITY msgsMenu.label "Messages">
 <!ENTITY msgsMenu.accesskey "M">
-<!ENTITY viewThreaded.label "Threaded">
-<!ENTITY viewThreaded.accesskey "T">
 <!ENTITY viewAll.label "All">
 <!ENTITY viewUnread.label "Unread">
 <!ENTITY viewAll.accesskey "A">
diff --git a/mailnews/base/resources/content/mail3PaneWindowCommands.js b/mailnews/base/resources/content/mail3PaneWindowCommands.js
index db3bb22b537..e756de77d1d 100644
--- a/mailnews/base/resources/content/mail3PaneWindowCommands.js
+++ b/mailnews/base/resources/content/mail3PaneWindowCommands.js
@@ -206,7 +206,6 @@ var DefaultController =
 			case "cmd_file":
 			case "cmd_emptyTrash":
 			case "cmd_compactFolder":
-			case "cmd_sortByThread":
   	  case "cmd_settingsOffline":
       case "cmd_close":
       case "cmd_selectAll":
@@ -369,7 +368,6 @@ var DefaultController =
       case "cmd_previousFlaggedMsg":
         return IsViewNavigationItemEnabled();
       case "cmd_viewAllMsgs":
-      case "cmd_sortByThread":
       case "cmd_viewUnreadMsgs":
       case "cmd_viewThreadsWithUnread":
       case "cmd_viewWatchedThreadsWithUnread":
@@ -514,9 +512,6 @@ var DefaultController =
 			case "cmd_previousFlaggedMsg":
 				MsgPreviousFlaggedMessage();
 				break;
-			case "cmd_sortByThread":
-				MsgSortByThread();
-				break;
 			case "cmd_viewAllMsgs":
       case "cmd_viewThreadsWithUnread":
       case "cmd_viewWatchedThreadsWithUnread":
diff --git a/mailnews/base/resources/content/mailWindowOverlay.js b/mailnews/base/resources/content/mailWindowOverlay.js
index 1f0b2a96e03..06daa7effa9 100644
--- a/mailnews/base/resources/content/mailWindowOverlay.js
+++ b/mailnews/base/resources/content/mailWindowOverlay.js
@@ -210,7 +210,6 @@ function InitViewSortByMenu()
     setSortByMenuItemCheckState("sortBySizeMenuitem", (sortType == nsMsgViewSortType.bySize));
     setSortByMenuItemCheckState("sortByStatusMenuitem", (sortType == nsMsgViewSortType.byStatus));
     setSortByMenuItemCheckState("sortBySubjectMenuitem", (sortType == nsMsgViewSortType.bySubject));
-    setSortByMenuItemCheckState("sortByThreadMenuitem", (sortType == nsMsgViewSortType.byThread));
     setSortByMenuItemCheckState("sortByUnreadMenuitem", (sortType == nsMsgViewSortType.byUnread));
     setSortByMenuItemCheckState("sortByLabelMenuitem", (sortType == nsMsgViewSortType.byLabel));
     setSortByMenuItemCheckState("sortByJunkStatusMenuitem", (sortType == nsMsgViewSortType.byJunkStatus));
@@ -222,8 +221,15 @@ function InitViewSortByMenu()
     setSortByMenuItemCheckState("sortAscending", (sortOrder == nsMsgViewSortOrder.ascending));
     setSortByMenuItemCheckState("sortDescending", (sortOrder == nsMsgViewSortOrder.descending));
 
-    var threadMenuItem = document.getElementById("sortByThreadMenuitem");
-    threadMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
+    var threaded = ((gDBView.viewFlags & nsMsgViewFlagsType.kThreadedDisplay) != 0);
+    var sortThreadedMenuItem = document.getElementById("sortThreaded");
+    var sortUnthreadedMenuItem = document.getElementById("sortUnthreaded");
+
+    sortThreadedMenuItem.setAttribute("checked", threaded);
+    sortUnthreadedMenuItem.setAttribute("checked", !threaded);
+
+    sortThreadedMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
+    sortUnthreadedMenuItem.setAttribute("disabled", !gDBView.supportsThreading);
 }
 
 function InitViewMessagesMenu()
@@ -254,12 +260,6 @@ function InitViewMessagesMenu()
 
 function InitViewMessageViewMenu()
 {
-  var viewFlags = gDBView ? gDBView.viewFlags : 0;
-
-	var threadedMenuItem = document.getElementById("viewThreaded");
-	if (threadedMenuItem)
-		threadedMenuItem.setAttribute("checked", (viewFlags & nsMsgViewFlagsType.kThreadedDisplay) != 0);
-
   var currentViewValue = document.getElementById("viewPicker").value;
 
   var allMenuItem = document.getElementById("viewAll");
diff --git a/mailnews/base/resources/content/mailWindowOverlay.xul b/mailnews/base/resources/content/mailWindowOverlay.xul
index 2810b8e2bca..c1f4843a78c 100644
--- a/mailnews/base/resources/content/mailWindowOverlay.xul
+++ b/mailnews/base/resources/content/mailWindowOverlay.xul
@@ -125,7 +125,6 @@ Rights Reserved.
    <command id="cmd_viewThreadsWithUnread" oncommand="goDoCommand('cmd_viewThreadsWithUnread')" disabled="true"/>
    <command id="cmd_viewWatchedThreadsWithUnread" oncommand="goDoCommand('cmd_viewWatchedThreadsWithUnread')" disabled="true"/>
    <command id="cmd_viewIgnoredThreads" oncommand="goDoCommand('cmd_viewIgnoredThreads')" disabled="true"/>
-   <command id="cmd_sortByThread" oncommand="goDoCommand('cmd_sortByThread')" disabled="true"/>
    <commandset id="viewZoomCommands"/>
 </commandset>
 
@@ -1185,19 +1184,19 @@ Rights Reserved.
           <menuitem id="sortBySizeMenuitem" type="radio" name="sortby" label="&sortBySizeCmd.label;" accesskey="&sortBySizeCmd.accesskey;" oncommand="MsgSortBySize()"/>
           <menuitem id="sortByStatusMenuitem" type="radio" name="sortby" label="&sortByStatusCmd.label;" accesskey="&sortByStatusCmd.accesskey;" oncommand="MsgSortByStatus()"/>
           <menuitem id="sortBySubjectMenuitem" type="radio" name="sortby" label="&sortBySubjectCmd.label;" accesskey="&sortBySubjectCmd.accesskey;" oncommand="MsgSortBySubject()"/>
-          <menuitem id="sortByThreadMenuitem" type="radio" name="sortby" label="&sortByThreadCmd.label;"  accesskey="&sortByThreadCmd.accesskey;" oncommand="MsgSortByThread()"/>
           <menuitem id="sortByUnreadMenuitem" type="radio" name="sortby" label="&sortByUnreadCmd.label;"  accesskey="&sortByUnreadCmd.accesskey;" oncommand="MsgSortByUnread()"/>
           <menuitem id="sortByLabelMenuitem" type="radio" name="sortby" label="&sortByLabelCmd.label;" accesskey="&sortByLabelCmd.accesskey;" oncommand="MsgSortByLabel()"/>
           <menuitem id="sortByJunkStatusMenuitem" type="radio" name="sortby" label="&sortByJunkStatusCmd.label;" accesskey="&sortByJunkStatusCmd.accesskey;" oncommand="MsgSortByJunkStatus()"/>
           <menuseparator/>
           <menuitem id="sortAscending" type="radio" name="sortdirection" label="&sortAscending.label;" accesskey="&sortAscending.accesskey;" oncommand="MsgSortAscending()"/>
           <menuitem id="sortDescending" type="radio" name="sortdirection" label="&sortDescending.label;" accesskey="&sortDescending.accesskey;" oncommand="MsgSortDescending()"/>
+          <menuseparator/>
+          <menuitem id="sortThreaded" type="radio" name="threaded" label="&sortThreaded.label;" accesskey="&sortThreaded.accesskey;" oncommand="MsgSortThreaded();"/>
+          <menuitem id="sortUnthreaded" type="radio" name="threaded" label="&sortUnthreaded.label;" accesskey="&sortUnthreaded.accesskey;" oncommand="MsgSortUnthreaded();"/>
         </menupopup>
       </menu>
       <menu label="&msgsMenu.label;" id="viewMessageViewMenu" accesskey="&msgsMenu.accesskey;">
         <menupopup id="viewMessageViewPopup" onpopupshowing="InitViewMessageViewMenu()">
-					<menuitem id="viewThreaded" type="checkbox" label="&viewThreaded.label;" accesskey="&viewThreaded.accesskey;" oncommand="MsgToggleThreaded();"/>
-          <menuseparator/>
           <menuitem id="viewAll" type="radio" name="viewmessages" label="&viewAll.label;" accesskey="&viewAll.accesskey;" oncommand="ViewMessagesBy('viewPickerAll');"/>
           <menuitem id="viewUnread" type="radio" name="viewmessages" label="&viewUnread.label;" accesskey="&viewUnread.accesskey;" oncommand="ViewMessagesBy('viewPickerUnread');"/>
           <menuseparator/>
diff --git a/mailnews/base/resources/content/threadPane.js b/mailnews/base/resources/content/threadPane.js
index 44cc05e9346..a6f702b1763 100644
--- a/mailnews/base/resources/content/threadPane.js
+++ b/mailnews/base/resources/content/threadPane.js
@@ -282,10 +282,24 @@ function MsgReverseSortThreadPane()
 
 function MsgToggleThreaded()
 {
-  var dbview = GetDBView();
-  dbview.viewFlags ^= nsMsgViewFlagsType.kThreadedDisplay;
-  dbview.sort(dbview.sortType, dbview.sortOrder); // resort
-  UpdateSortIndicators(dbview.sortType, dbview.sortOrder);
+    var dbview = GetDBView();
+    dbview.viewFlags ^= nsMsgViewFlagsType.kThreadedDisplay;
+    dbview.sort(dbview.sortType, dbview.sortOrder);
+    UpdateSortIndicators(dbview.sortType, dbview.sortOrder);
+}
+
+function MsgSortThreaded()
+{
+    // Toggle if not already threaded.
+    if ((GetDBView().viewFlags & nsMsgViewFlagsType.kThreadedDisplay) == 0)
+        MsgToggleThreaded();
+}
+
+function MsgSortUnthreaded()
+{
+    // Toggle if not already unthreaded.
+    if ((GetDBView().viewFlags & nsMsgViewFlagsType.kThreadedDisplay) != 0)
+        MsgToggleThreaded();
 }
 
 function MsgSortAscending()
diff --git a/mailnews/base/resources/locale/en-US/messenger.dtd b/mailnews/base/resources/locale/en-US/messenger.dtd
index 38a5e442421..3faf80871ec 100644
--- a/mailnews/base/resources/locale/en-US/messenger.dtd
+++ b/mailnews/base/resources/locale/en-US/messenger.dtd
@@ -170,18 +170,18 @@ Rights Reserved.
 <!ENTITY sortByRecipientCmd.accesskey "c">
 <!ENTITY sortByUnreadCmd.label "Read">
 <!ENTITY sortByUnreadCmd.accesskey "R">
-<!ENTITY sortByThreadCmd.label "Thread">
-<!ENTITY sortByThreadCmd.accesskey "T">
 <!ENTITY sortByOrderReceivedCmd.label "Order Received">
 <!ENTITY sortByOrderReceivedCmd.accesskey "O">
 <!ENTITY sortAscending.label "Ascending">
 <!ENTITY sortAscending.accesskey "A">
 <!ENTITY sortDescending.label "Descending">
 <!ENTITY sortDescending.accesskey "D">
+<!ENTITY sortThreaded.label "Threaded">
+<!ENTITY sortThreaded.accesskey "T">
+<!ENTITY sortUnthreaded.label "Unthreaded">
+<!ENTITY sortUnthreaded.accesskey "h">
 <!ENTITY msgsMenu.label "Messages">
 <!ENTITY msgsMenu.accesskey "M">
-<!ENTITY viewThreaded.label "Threaded">
-<!ENTITY viewThreaded.accesskey "T">
 <!ENTITY viewAll.label "All">
 <!ENTITY viewUnread.label "Unread">
 <!ENTITY viewAll.accesskey "A">