Bug 570046 Fix test_update.js hanging on apps/build configs that don't support lightweight themes. r=dtownsend

toolkit/mozapps/extensions/test/xpcshell/test_update.js

@@ -6,6 +6,9 @@
 
 // The test extension uses an insecure update url.
 Services.prefs.setBoolPref("extensions.checkUpdateSecurity", false);
+// This test requires lightweight themes update to be enabled even if the app
+// doesn't support lightweight themes.
+Services.prefs.setBoolPref("lightweightThemes.update.enabled", true);
 
 Components.utils.import("resource://gre/modules/LightweightThemeManager.jsm");