Bug 400372 New composer page isn't unmodified r=glazou

editor/ui/composer/content/editor.js

@@ -2476,14 +2476,10 @@ function EditorSetDefaultPrefsAndDoctype()
     catch (ex) {}
     if ( prefCharsetString && prefCharsetString != 0)
     {
-        element = domdoc.createElement("meta");
-        if ( element )
-        {
-          element.setAttribute("http-equiv", "content-type");
-          element.setAttribute("content", "text/html; charset=" + prefCharsetString);
-          headelement.insertBefore( element, headelement.firstChild );
-          editor.documentCharacterSet = prefCharsetString;
-        }
+      editor.enableUndo(false);
+      editor.documentCharacterSet = prefCharsetString;
+      editor.resetModificationCount();
+      editor.enableUndo(true);
     }
 
     var node = 0;