Bug 382349 - address review comment about making sense of the comment explaining why we .focus() twice to shift focus once

mail/base/content/mail3PaneWindowCommands.js

@@ -992,7 +992,9 @@ function SetFocusThreadPane()
 
 function SetFocusMessagePane()
 {
-  // messagePaneFrame.focus() fails to blur the currently focused element
+  // Calling .focus() on content doesn't blur the previously focused chrome
+  // element, so we shift focus to the XUL pane first, to not leave another
+  // pane looking like it has focus.
   GetMessagePane().focus();
   GetMessagePaneFrame().focus();
 }