Port Bug #303288 from firefox to thunderbird --> Advanced > Updates > Extensions > Check now opens extension manager without close button

mail/components/preferences/advanced.js

@@ -195,7 +195,7 @@ var gAdvancedPane = {
         getService(Components.interfaces.nsIWindowMediator);
     var manager = wm.getMostRecentWindow("Extension:Manager-extensions");
     if (!manager) {
-      const features = "chrome,centerscreen,dialog,titlebar";
+      const features = "chrome,dialog=no,resizable";
       const URI_EXTENSIONS_WINDOW = 
         "chrome://mozapps/content/extensions/extensions.xul?type=extensions";
       openDialog(URI_EXTENSIONS_WINDOW, "", features, "updatecheck");