diff --git a/calendar/resources/content/calendar.js b/calendar/resources/content/calendar.js
index 153198bcfad2..d2ae21677596 100644
--- a/calendar/resources/content/calendar.js
+++ b/calendar/resources/content/calendar.js
@@ -334,7 +334,7 @@ function launchPreferences()
   if( applicationName == "Mozilla" || applicationName == "Firebird" ) {
     goPreferences( "calendarPanel", "chrome://calendar/content/pref/calendarPref.xul", "calendarPanel" );
   } else
-    window.openDialog("chrome://calendar/content/pref/prefBird.xul", "PrefWindow", "chrome,titlebar,modal,resizable=no");
+    window.openDialog("chrome://calendar/content/pref/prefBird.xul", "PrefWindow", "chrome,titlebar,modal,resizable,modal");
 }
 
 /**