diff --git a/chrome/src/nsChromeRegistryChrome.cpp b/chrome/src/nsChromeRegistryChrome.cpp
index 0c2252d1905..8031eef70f1 100644
--- a/chrome/src/nsChromeRegistryChrome.cpp
+++ b/chrome/src/nsChromeRegistryChrome.cpp
@@ -36,6 +36,7 @@
 #include "nsIObserverService.h"
 #include "nsIPrefBranch.h"
 #include "nsIPrefService.h"
+#include "mozilla/Preferences.h"
 #include "nsIResProtocolHandler.h"
 #include "nsIScriptError.h"
 #include "nsIVersionComparator.h"
@@ -48,6 +49,7 @@
 #define MATCH_OS_LOCALE_PREF "intl.locale.matchOS"
 #define SELECTED_LOCALE_PREF "general.useragent.locale"
 #define SELECTED_SKIN_PREF   "general.skins.selectedSkin"
+#define PACKAGE_OVERRIDE_BRANCH "chrome.override_package."
 
 using namespace mozilla;
 
@@ -196,20 +198,25 @@ NS_IMETHODIMP
 nsChromeRegistryChrome::GetLocalesForPackage(const nsACString& aPackage,
                                        nsIUTF8StringEnumerator* *aResult)
 {
+  nsCString realpackage;
+  nsresult rv = OverrideLocalePackage(aPackage, realpackage);
+  if (NS_FAILED(rv))
+    return rv;
+
   nsTArray<nsCString> *a = new nsTArray<nsCString>;
   if (!a)
     return NS_ERROR_OUT_OF_MEMORY;
 
   PackageEntry* entry =
       static_cast<PackageEntry*>(PL_DHashTableOperate(&mPackagesHash,
-                                                      & aPackage,
+                                                      & realpackage,
                                                       PL_DHASH_LOOKUP));
 
   if (PL_DHASH_ENTRY_IS_BUSY(entry)) {
     entry->locales.EnumerateToArray(a);
   }
 
-  nsresult rv = NS_NewAdoptingUTF8StringEnumerator(aResult, a);
+  rv = NS_NewAdoptingUTF8StringEnumerator(aResult, a);
   if (NS_FAILED(rv))
     delete a;
 
@@ -267,9 +274,13 @@ nsresult
 nsChromeRegistryChrome::GetSelectedLocale(const nsACString& aPackage,
                                           nsACString& aLocale)
 {
+  nsCString realpackage;
+  nsresult rv = OverrideLocalePackage(aPackage, realpackage);
+  if (NS_FAILED(rv))
+    return rv;
   PackageEntry* entry =
       static_cast<PackageEntry*>(PL_DHashTableOperate(&mPackagesHash,
-                                                      & aPackage,
+                                                      & realpackage,
                                                       PL_DHASH_LOOKUP));
 
   if (PL_DHASH_ENTRY_IS_FREE(entry))
@@ -282,6 +293,21 @@ nsChromeRegistryChrome::GetSelectedLocale(const nsACString& aPackage,
   return NS_OK;
 }
 
+nsresult
+nsChromeRegistryChrome::OverrideLocalePackage(const nsACString& aPackage,
+                                              nsACString& aOverride)
+{
+  const nsACString& pref = NS_LITERAL_CSTRING(PACKAGE_OVERRIDE_BRANCH) + aPackage;
+  nsAdoptingCString override = mozilla::Preferences::GetCString(PromiseFlatCString(pref).get());
+  if (override) {
+    aOverride = override;
+  }
+  else {
+    aOverride = aPackage;
+  }
+  return NS_OK;
+}
+
 nsresult
 nsChromeRegistryChrome::SelectLocaleFromPref(nsIPrefBranch* prefs)
 {
diff --git a/chrome/src/nsChromeRegistryChrome.h b/chrome/src/nsChromeRegistryChrome.h
index 211b54a79c9..57d3e6cb8b6 100644
--- a/chrome/src/nsChromeRegistryChrome.h
+++ b/chrome/src/nsChromeRegistryChrome.h
@@ -50,6 +50,8 @@ class nsChromeRegistryChrome : public nsChromeRegistry
                                          PLDHashEntryHdr *entry,
                                          uint32_t number, void *arg);
 
+  nsresult OverrideLocalePackage(const nsACString& aPackage,
+                                 nsACString& aOverride);
   nsresult SelectLocaleFromPref(nsIPrefBranch* prefs);
   nsresult UpdateSelectedLocale() MOZ_OVERRIDE;
   nsIURI* GetBaseURIFromPackage(const nsCString& aPackage,
diff --git a/chrome/test/unit/data/test_bug848297.manifest b/chrome/test/unit/data/test_bug848297.manifest
new file mode 100644
index 00000000000..d9730a9ce75
--- /dev/null
+++ b/chrome/test/unit/data/test_bug848297.manifest
@@ -0,0 +1,4 @@
+locale basepack en-US jar:en-US.jar!/locale/en-US/global/
+locale basepack fr jar:en-US.jar!/locale/en-US/global/
+locale overpack en-US jar:en-US.jar!/locale/en-US/global/
+locale overpack de jar:en-US.jar!/locale/en-US/global/
diff --git a/chrome/test/unit/test_bug848297.js b/chrome/test/unit/test_bug848297.js
new file mode 100644
index 00000000000..0875370f791
--- /dev/null
+++ b/chrome/test/unit/test_bug848297.js
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+var MANIFESTS = [
+  do_get_file("data/test_bug848297.manifest")
+];
+
+// Stub in the locale service so we can control what gets returned as the OS locale setting
+Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+registerManifests(MANIFESTS);
+
+var chromeReg = Cc["@mozilla.org/chrome/chrome-registry;1"]
+                .getService(Ci.nsIXULChromeRegistry)
+                .QueryInterface(Ci.nsIToolkitChromeRegistry);
+chromeReg.checkForNewChrome();
+
+var prefService = Cc["@mozilla.org/preferences-service;1"]
+                  .getService(Ci.nsIPrefService)
+                  .QueryInterface(Ci.nsIPrefBranch);
+
+function enum_to_array(strings) {
+  let rv = [];
+  while (strings.hasMore()) {
+    rv.push(strings.getNext());
+  }
+  rv.sort();
+  return rv;
+}
+
+function run_test() {
+
+  // without override
+  prefService.setCharPref("general.useragent.locale", "de");
+  do_check_eq(chromeReg.getSelectedLocale("basepack"), "en-US");
+  do_check_eq(chromeReg.getSelectedLocale("overpack"), "de");
+  do_check_matches(enum_to_array(chromeReg.getLocalesForPackage("basepack")),
+                   ['en-US', 'fr']);
+
+  // with override
+  prefService.setCharPref("chrome.override_package.basepack", "overpack");
+  do_check_eq(chromeReg.getSelectedLocale("basepack"), "de");
+  do_check_matches(enum_to_array(chromeReg.getLocalesForPackage("basepack")),
+                   ['de', 'en-US']);
+
+}
diff --git a/chrome/test/unit/xpcshell.ini b/chrome/test/unit/xpcshell.ini
index da5f4df5973..2134d8d95bf 100644
--- a/chrome/test/unit/xpcshell.ini
+++ b/chrome/test/unit/xpcshell.ini
@@ -11,6 +11,7 @@ tail =
 [test_bug415367.js]
 [test_bug519468.js]
 [test_bug564667.js]
+[test_bug848297.js]
 [test_crlf.js]
 [test_data_protocol_registration.js]
 [test_no_remote_registration.js]