diff --git a/extensions/firefox/components/PdfStreamConverter.js b/extensions/firefox/components/PdfStreamConverter.js
index f4b5b7712..af9cf41b8 100644
--- a/extensions/firefox/components/PdfStreamConverter.js
+++ b/extensions/firefox/components/PdfStreamConverter.js
@@ -58,6 +58,9 @@ ChromeActions.prototype = {
       return '{}';
     return application.prefs.getValue(EXT_PREFIX + '.database', '{}');
   },
+  getLocale: function() {
+    return application.prefs.getValue('general.useragent.locale', 'en-US');
+  },
   pdfBugEnabled: function() {
     return application.prefs.getValue(EXT_PREFIX + '.pdfBugEnabled', false);
   }
diff --git a/external/webL10n/l10n.js b/external/webL10n/l10n.js
index bb847ee10..832f0819c 100644
--- a/external/webL10n/l10n.js
+++ b/external/webL10n/l10n.js
@@ -18,7 +18,11 @@
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
   * IN THE SOFTWARE.
   */
-
+/*
+  Additional modifications for PDF.js project:
+    - Loading resources from <script type='application/l10n'>;
+    - Disabling language assignment on page loading.
+*/
 'use strict';
 
 (function(window) {
@@ -271,6 +275,7 @@
     gLanguage = '';
   }
 
+  /*
   // load the default locale on startup
   window.addEventListener('DOMContentLoaded', function() {
     var lang = navigator.language;
@@ -286,6 +291,7 @@
       loadLocale(lang, translateFragment);
     }
   });
+  */
 
   // Public API
   document.mozL10n = {
diff --git a/web/viewer.js b/web/viewer.js
index be848cd70..e262a6b87 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -1347,8 +1347,11 @@ window.addEventListener('load', function webViewerLoad(evt) {
   if ('disableWorker' in hashParams)
     PDFJS.disableWorker = (hashParams['disableWorker'] === 'true');
 
+  var locale = !PDFJS.isFirefoxExtension ? navigator.language :
+    FirefoxCom.request('getLocale', null);
   if ('locale' in hashParams)
-    mozL10n.language.code = hashParams['locale'];
+    locale = hashParams['locale'];
+  mozL10n.language.code = locale;
 
   if ('disableTextLayer' in hashParams)
     PDFJS.disableTextLayer = (hashParams['disableTextLayer'] === 'true');