diff --git a/toolkit/modules/UpdateUtils.jsm b/toolkit/modules/UpdateUtils.jsm
index 80cddfd369..31a9e933e0 100644
--- a/toolkit/modules/UpdateUtils.jsm
+++ b/toolkit/modules/UpdateUtils.jsm
@@ -66,6 +66,7 @@ this.UpdateUtils = {
     let custom = prefBranch.getCharPref(PREF_APP_UPDATE_CUSTOM, "");
     let distribution = prefBranch.getCharPref(PREF_APP_DISTRIBUTION, "default");
     let distributionVersion = prefBranch.getCharPref(PREF_APP_DISTRIBUTION_VERSION, "default");
+    let navigator = Services.appShell.hiddenDOMWindow.navigator;
 
     let substs = [
       [/%ID%/g,                     Services.appinfo.ID],