Make sure the _main_ window is focussed (closes #1484138).

program/js/app.js

@@ -203,7 +203,10 @@ function rcube_webmail()
 
         this.set_page_buttons();
 
-        // focus this window
+        // focus main window
+        if (this.env.framed && window.parent)
+          window.parent.focus();
+        else
           window.focus();
 
         // init message compose form