Bug 69600: ``Header "Mail Folders" disappears in alternate 3-pane layout'', author=ksosez, r=timeless, sr=sspitzer

mailnews/base/resources/content/mail3PaneWindowVertLayout.xul

@@ -138,7 +138,10 @@ Rights Reserved.
           
     <box orient="vertical" flex="1">
       <box id="mail3PaneVertLayoutBox" orient="horizontal" persist="collapsed height" flex="1">
-        <tree id="folderTree" flex="1" style="width:0px;" context="folderPaneContext" persist="collapsed width"/>
+        <box orient="vertical" flex="1" autostrech="always" persist="width">
+          <sidebarheader type="box" class="sidebarheader-main" label="&mail-sidebar-header.label;"/>
+          <tree id="folderTree" flex="1" style="width:0px;" context="folderPaneContext" persist="collapsed width"/>
+        </box>
         <splitter id="gray_vertical_splitter" collapse="before"  persist="state">
           <grippy/>
         </splitter>