mail shell needs a frame for browser.webwindow

mailnews/ui/messenger/resources/mailshell.html

@@ -23,7 +23,7 @@ BODY {
 
 <iframe src="msgbar.xml" name="browser.toolbar" width="100%" height="56" >
 
-<iframe src="frames.html" name="browser.tree" width="100%" height="500" >
+<iframe src="frames.html" name="browser.webwindow" width="100%" height="500" >
 
 <iframe src="status.html" name="browser.status" width="100%" height="34" >