diff --git a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
index 0fb2ae28b62..5dba529906d 100644
--- a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
+++ b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
@@ -12,7 +12,7 @@ queryUninstallExtensionMessage=If you uninstall %S, the functionality it offers
 queryUninstallThemeMessage=Do you want to uninstall %S?
 queryUninstallTitle=Uninstall %S
 
-extensions.update.url=https://addons.mozilla.org/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&appID=%APP_ID%&appVersion=%APP_VERSION%
+extensions.update.url=https://addons.mozilla.org/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&appID=%APP_ID%&appVersion=%APP_VERSION%&appOS=%APP_OS%
 extensions.getMoreExtensionsURL=https://addons.mozilla.org/extensions/?application=%APPID%
 extensions.getMoreThemesURL=https://addons.mozilla.org/themes/?application=%APPID%
 
diff --git a/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in b/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
index b68bf1f3654..05b790feb8e 100644
--- a/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
+++ b/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
@@ -75,6 +75,7 @@ const FILE_CHROME_MANIFEST            = "contents.rdf";
 const FILE_WASINSAFEMODE              = "Safe Mode";
 const FILE_INSTALLED_EXTENSIONS       = "installed-extensions.txt"
 const FILE_INSTALLED_EXTENSIONS_PROCESSED = "installed-extensions-processed.txt"
+#expand const TARGET_OS                                 = "__OSARCH__";
 
 const KEY_PROFILEDIR                  = "ProfD";
 const KEY_APPDIR                      = "XCurProcD";
@@ -3112,6 +3113,7 @@ nsRDFItemUpdater.prototype = {
     dsURI = dsURI.replace(/%APP_ID%/g, this._updater._appID);
     dsURI = dsURI.replace(/%APP_VERSION%/g, this._updater._appVersion);
     dsURI = dsURI.replace(/%REQ_VERSION%/g, 1);
+    dsURI = dsURI.replace(/%APP_OS%/g, TARGET_OS);
     
     // escape() does not properly encode + symbols in any embedded FVF strings.
     dsURI = dsURI.replace(/\+/g, "%2B");