Construct update URL using RegExps per suggestion from Ben.

Include "0" in baseURL per Chase.

browser/app/profile/firefox.js

@@ -80,7 +80,7 @@ pref("app.update.autoInstallMode", 0);
 
 // XXX these prefs and others like them are distribution specific and should move 
 //     into chrome://browser
-pref("app.update.url.base", "https://aus.mozilla.org/update/");
+pref("app.update.url", "chrome://mozapps/locale/update/updates.properties");
 pref("app.update.url.manual", "chrome://mozapps/locale/update/updates.properties");
 pref("app.update.url.override", "chrome://mozapps/locale/update/updates.properties");
 pref("app.update.updatesAvailable", false);

toolkit/locales/en-US/chrome/mozapps/update/updates.properties

@@ -4,11 +4,15 @@ updateType_minor=Security Update
 introType_minor=An important Security Update for %S is available:
 introType_major=A new version of %S is available:
 verificationError=%S could not confirm the integrity of the update package.
-app.update.url.manual=http://www.mozilla.org/update
-# This should be empty unless you wish to override the URL used to discover
-# available updates.
-app.update.url.override=
 errorsPageHeader=Update Failed
 IAgreeLabel=I Agree
 license404Error=The license file could not be found. Please contact the distributor.
 downloadingLicense=Downloading license text...
+# The prefix /update2/0/ uniquely identifies the format of this URL.  If you
+# change the format of this URL, then you MUST change the prefix (i.e.,
+# increment 0 to 1).
+app.update.url=https://aus.mozilla.org/update2/0/%PRODUCT%/%VERSION%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/update.xml
+# When updating fails, we present the user with this web page:
+app.update.url.manual=http://www.mozilla.org/update
+# This value should be empty unless you wish to override app.update.url
+app.update.url.override=

toolkit/mozapps/update/src/nsUpdateService.js.in

@@ -49,7 +49,7 @@ const PREF_APP_UPDATE_INTERVAL            = "app.update.interval";
 const PREF_APP_UPDATE_TIMER               = "app.update.timer";
 const PREF_APP_UPDATE_LOG_ENABLED         = "app.update.logEnabled";
 
-const PREF_APP_UPDATE_URL_BASE            = "app.update.url.base";
+const PREF_APP_UPDATE_URL                 = "app.update.url";
 const PREF_APP_UPDATE_URL_OVERRIDE        = "app.update.url.override";
 
 const PREF_UPDATE_LASTUPDATETIME_FMT      = "app.update.lastUpdateTime.%ID%";
@@ -974,19 +974,22 @@ Checker.prototype = {
     } catch (e) {}
 
     // Otherwise, construct the update URL from component parts.
-    var baseURL = getPref("getCharPref", PREF_APP_UPDATE_URL_BASE, null);
-    if (!baseURL) {
-      LOG(PREF_APP_UPDATE_URL_BASE + " not defined");
+    try {
+      url = gPref.getComplexValue(PREF_APP_UPDATE_URL,
+                                  nsIPrefLocalizedString).data;
+    } catch (e) {
+      LOG(PREF_APP_UPDATE_URL + " not defined");
       return null;
     }
 
-    // <product-name>/<version>/<build-id>/<build-target>/<locale>/update.xml
-    url = baseURL +
-        gApp.name + "/" +
-        gApp.version + "/" +
-        gApp.appBuildID + "/" +
-        gApp.OS + "_" + gApp.XPCOMABI + "/" +
-        gPref.getCharPref("general.useragent.locale") + "/update.xml";
+    var locale = gPref.getCharPref("general.useragent.locale");
+
+    url = url.replace(/%PRODUCT%/g, gApp.name);
+    url = url.replace(/%VERSION%/g, gApp.version);
+    url = url.replace(/%BUILD_ID%/g, gApp.appBuildID);
+    url = url.replace(/%BUILD_TARGET%/g, gApp.OS + "_" + gApp.XPCOMABI);
+    url = url.replace(/%LOCALE%/g, locale);
+
     LOG("update url: " + url);
     return url;
   },