diff --git a/web/viewer.js b/web/viewer.js
index c56aff64b..dc748025f 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -1332,6 +1332,37 @@ window.PDFView = PDFViewerApplication; // obsolete name, using it as an alias
 //})();
 //#endif
 
+//#if GENERIC
+var HOSTED_VIEWER_ORIGINS = ['null',
+  'http://mozilla.github.io', 'https://mozilla.github.io'];
+function validateFileURL(file) {
+  try {
+    var viewerOrigin = new URL(window.location.href).origin || 'null';
+    if (HOSTED_VIEWER_ORIGINS.indexOf(viewerOrigin) >= 0) {
+      // Hosted or local viewer, allow for any file locations
+      return;
+    }
+    var fileOrigin = new URL(file, window.location.href).origin;
+    // Removing of the following line will not guarantee that the viewer will
+    // start accepting URLs from foreign origin -- CORS headers on the remote
+    // server must be properly configured.
+    if (fileOrigin !== viewerOrigin) {
+      throw new Error('file origin does not match viewer\'s');
+    }
+  } catch (e) {
+    var message = e && e.message;
+    var loadingErrorMessage = mozL10n.get('loading_error', null,
+      'An error occurred while loading the PDF.');
+
+    var moreInfo = {
+      message: message
+    };
+    PDFViewerApplication.error(loadingErrorMessage, moreInfo);
+    throw e;
+  }
+}
+//#endif
+
 function webViewerLoad(evt) {
 //#if !PRODUCTION
   require.config({paths: {'pdfjs': '../src'}});
@@ -1351,6 +1382,7 @@ function webViewerInitialized() {
   var queryString = document.location.search.substring(1);
   var params = parseQueryString(queryString);
   var file = 'file' in params ? params.file : DEFAULT_URL;
+  validateFileURL(file);
 //#endif
 //#if (FIREFOX || MOZCENTRAL)
 //var file = window.location.href.split('#')[0];