diff --git a/chrome/src/nsChromeRegistry.cpp b/chrome/src/nsChromeRegistry.cpp

--- a/chrome/src/nsChromeRegistry.cpp

+++ b/chrome/src/nsChromeRegistry.cpp

@@ -1267,20 +1267,21 @@ nsChromeRegistry::WrappersEnabled(nsIURI

   return PL_DHASH_ENTRY_IS_LIVE(entry) &&

          entry->flags & PackageEntry::XPCNATIVEWRAPPERS;

 }

 nsresult

 nsChromeRegistry::SelectLocaleFromPref(nsIPrefBranch* prefs)

 {

   nsresult rv;

-  PRBool matchOSLocale = PR_FALSE;

+  PRBool matchOSLocale = PR_FALSE, userLocaleOverride = PR_FALSE;

+  prefs->PrefHasUserValue(SELECTED_LOCALE_PREF, &userLocaleOverride);

   rv = prefs->GetBoolPref(MATCH_OS_LOCALE_PREF, &matchOSLocale);

-  if (NS_SUCCEEDED(rv) && matchOSLocale) {

+  if (NS_SUCCEEDED(rv) && matchOSLocale && !userLocaleOverride) {

     // compute lang and region code only when needed!

     nsCAutoString uiLocale;

     rv = getUILangCountry(uiLocale);

     if (NS_SUCCEEDED(rv))

       mSelectedLocale = uiLocale;

   }

   else {

     nsXPIDLCString provider;

diff --git a/chrome/test/unit/data/test_bug519468.manifest b/chrome/test/unit/data/test_bug519468.manifest

deleted file mode 100644

--- a/chrome/test/unit/data/test_bug519468.manifest

+++ /dev/null

@@ -1,2 +0,0 @@

-locale testmatchos en-US jar:en-US.jar!/locale/en-US/global/

-locale testmatchos fr-FR jar:en-US.jar!/locale/en-US/global/

diff --git a/chrome/test/unit/test_bug519468.js b/chrome/test/unit/test_bug519468.js

--- a/chrome/test/unit/test_bug519468.js

+++ b/chrome/test/unit/test_bug519468.js

@@ -31,50 +31,90 @@

  * decision by deleting the provisions above and replace them with the notice

  * and other provisions required by the GPL or the LGPL. If you do not delete

  * the provisions above, a recipient may use your version of this file under

  * the terms of any one of the MPL, the GPL or the LGPL.

  *

  * ***** END LICENSE BLOCK *****

  */

+function write_locale(stream, locale, package) {

+  var s = "locale " + package + " " + locale + " jar:" + locale + ".jar!";

+  s += "/locale/" + locale + "/" + package +"/\n";

+  stream.write(s, s.length);

+}

+

+var localeService = Cc["@mozilla.org/intl/nslocaleservice;1"]

+                    .getService(Ci.nsILocaleService);

+

+var systemLocale = localeService.getLocaleComponentForUserAgent();

+

+var locales;

+

+if (systemLocale == "en-US")

+  locales = [ "en-US", "fr-FR", "de-DE" ];

+else if (systemLocale == "fr-FR")

+  locales = [ "en-US", systemLocale, "de-DE" ];

+else

+  locales = [ "en-US", systemLocale, "fr-FR" ];

+

+var workingDir = Cc["@mozilla.org/file/directory_service;1"].

+                 getService(Ci.nsIProperties).get("TmpD", Ci.nsIFile);

+var manifest = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsILocalFile);

+manifest.initWithFile(workingDir);

+manifest.append("test_bug519468.manifest");

+manifest.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0600);

+var stream = Cc["@mozilla.org/network/file-output-stream;1"].

+             createInstance(Ci.nsIFileOutputStream);

+stream.init(manifest, 0x04 | 0x08 | 0x20, 0600, 0); // write, create, truncate

+locales.slice(0,2).forEach(function(l) write_locale(stream, l, "testmatchos"));

+write_locale(stream, locales[2], "testnomatchos");

+stream.close();

+

 var MANIFESTS = [

-  do_get_file("data/test_bug519468.manifest")

+  manifest

 ];

 registerManifests(MANIFESTS);

 var chromeReg = Cc["@mozilla.org/chrome/chrome-registry;1"]

                 .getService(Ci.nsIXULChromeRegistry)

                 .QueryInterface(Ci.nsIToolkitChromeRegistry);

-var localeService = Cc["@mozilla.org/intl/nslocaleservice;1"]

-                    .getService(Ci.nsILocaleService);

-

 var prefService = Cc["@mozilla.org/preferences-service;1"]

                   .getService(Ci.nsIPrefService)

                   .QueryInterface(Ci.nsIPrefBranch);

 function test_locale(aTest) {

   prefService.setBoolPref("intl.locale.matchOS", aTest.matchOS);

-  prefService.setCharPref("general.useragent.locale", aTest.selected || "en-US");

+  if (aTest.selected)

+    prefService.setCharPref("general.useragent.locale", aTest.selected);

+  else

+    try {

+      prefService.clearUserPref("general.useragent.locale");

+    } catch(e) {}

-  var selectedLocale = chromeReg.getSelectedLocale("testmatchos");

+  var selectedLocale = chromeReg.getSelectedLocale(aTest.package);

   do_check_eq(selectedLocale, aTest.locale);

 }

 function run_test()

 {

-  var systemLocale = localeService.getLocaleComponentForUserAgent();

-

   var tests = [

-    {matchOS: false, selected: null, locale: "en-US"},

     {matchOS: true, selected: null, locale: systemLocale},

-    {matchOS: true, selected: "fr-FR", locale: systemLocale},

-    {matchOS: false, selected: "fr-FR", locale: "fr-FR"},

-    {matchOS: true, selected: null, locale: systemLocale}

+    {matchOS: true, selected: locales[0], locale: locales[0]},

+    {matchOS: true, selected: locales[1], locale: locales[1]},

+    {matchOS: true, selected: locales[2], locale: locales[0]},

+    {matchOS: true, selected: null, locale: locales[2], package: "testnomatchos"},

+    {matchOS: false, selected: null, locale: locales[0]},

+    {matchOS: false, selected: locales[0], locale: locales[0]},

+    {matchOS: false, selected: locales[1], locale: locales[1]},

+    {matchOS: false, selected: locales[2], locale: locales[0]},

   ];

   for (var i = 0; i < tests.length; ++ i) {

     var test = tests[i];

+    if (!test.package)

+      test.package = "testmatchos";

     test_locale(test);

   }

+  manifest.remove(false);

 }