diff --git a/extensions/firefox/content/PdfJs.jsm b/extensions/firefox/content/PdfJs.jsm
index cbde0b77e..fd905086c 100644
--- a/extensions/firefox/content/PdfJs.jsm
+++ b/extensions/firefox/content/PdfJs.jsm
@@ -49,6 +49,8 @@ ChromeUtils.defineModuleGetter(this, "PdfjsChromeUtils",
                                "resource://pdf.js/PdfjsChromeUtils.jsm");
 ChromeUtils.defineModuleGetter(this, "PdfjsContentUtils",
                                "resource://pdf.js/PdfjsContentUtils.jsm");
+ChromeUtils.defineModuleGetter(this, "PdfJsDefaultPreferences",
+  "resource://pdf.js/PdfJsDefaultPreferences.jsm");
 
 function getBoolPref(aPref, aDefaultValue) {
   try {
@@ -75,18 +77,10 @@ function isDefaultHandler() {
 }
 
 function initializeDefaultPreferences() {
-  /* eslint-disable semi */
-  var DEFAULT_PREFERENCES =
-//#include ../../../web/default_preferences.json
-//#if false
-    "end of DEFAULT_PREFERENCES"
-//#endif
-  /* eslint-enable semi */
-
   var defaultBranch = Services.prefs.getDefaultBranch(PREF_PREFIX + ".");
   var defaultValue;
-  for (var key in DEFAULT_PREFERENCES) {
-    defaultValue = DEFAULT_PREFERENCES[key];
+  for (var key in PdfJsDefaultPreferences) {
+    defaultValue = PdfJsDefaultPreferences[key];
     switch (typeof defaultValue) {
       case "boolean":
         defaultBranch.setBoolPref(key, defaultValue);
diff --git a/extensions/firefox/content/PdfJsDefaultPreferences.jsm b/extensions/firefox/content/PdfJsDefaultPreferences.jsm
new file mode 100644
index 000000000..fb640c744
--- /dev/null
+++ b/extensions/firefox/content/PdfJsDefaultPreferences.jsm
@@ -0,0 +1,21 @@
+/* Copyright 2018 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["PdfJsDefaultPreferences"];
+
+var PdfJsDefaultPreferences =
+  Object.freeze(PDFJSDev.json("$ROOT/web/default_preferences.json"));
diff --git a/extensions/firefox/content/PdfjsChromeUtils.jsm b/extensions/firefox/content/PdfjsChromeUtils.jsm
index 067c18868..f045d44df 100644
--- a/extensions/firefox/content/PdfjsChromeUtils.jsm
+++ b/extensions/firefox/content/PdfjsChromeUtils.jsm
@@ -23,23 +23,18 @@ const PDF_CONTENT_TYPE = "application/pdf";
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.import("resource://gre/modules/Services.jsm");
 
+ChromeUtils.defineModuleGetter(this, "PdfJsDefaultPreferences",
+  "resource://pdf.js/PdfJsDefaultPreferences.jsm");
+
 var Svc = {};
 XPCOMUtils.defineLazyServiceGetter(Svc, "mime",
                                    "@mozilla.org/mime;1",
                                    "nsIMIMEService");
 
-/* eslint-disable semi */
-var DEFAULT_PREFERENCES =
-//#include ../../../web/default_preferences.json
-//#if false
-  "end of DEFAULT_PREFERENCES"
-//#endif
-/* eslint-enable semi */
-
 var PdfjsChromeUtils = {
   // For security purposes when running remote, we restrict preferences
   // content can access.
-  _allowedPrefNames: Object.keys(DEFAULT_PREFERENCES),
+  _allowedPrefNames: Object.keys(PdfJsDefaultPreferences),
   _ppmm: null,
   _mmg: null,
 
diff --git a/gulpfile.js b/gulpfile.js
index 54ef27640..ae92c8f22 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -700,6 +700,21 @@ gulp.task('minified-post', ['minified-pre'], function () {
 
 gulp.task('minified', ['minified-post']);
 
+function preprocessDefaultPreferences(content) {
+  var preprocessor2 = require('./external/builder/preprocessor2.js');
+  var licenseHeader = fs.readFileSync('./src/license_header.js').toString();
+
+  var MODIFICATION_WARNING =
+    '//\n// THIS FILE IS AUTOMATICALLY GENERATED, DO NOT EDIT MANUALLY!\n//\n';
+
+  content = preprocessor2.preprocessPDFJSCode({
+    rootPath: __dirname,
+    defines: DEFINES,
+  }, content);
+
+  return licenseHeader + '\n' + MODIFICATION_WARNING + '\n' + content;
+}
+
 gulp.task('firefox-pre', ['buildnumber', 'locale'], function () {
   console.log();
   console.log('### Building Firefox extension');
@@ -759,6 +774,10 @@ gulp.task('firefox-pre', ['buildnumber', 'locale'], function () {
         .pipe(gulp.dest(FIREFOX_BUILD_DIR)),
     gulp.src('LICENSE').pipe(gulp.dest(FIREFOX_BUILD_DIR)),
 
+    gulp.src(FIREFOX_CONTENT_DIR + 'PdfJsDefaultPreferences.jsm')
+        .pipe(transform('utf8', preprocessDefaultPreferences))
+        .pipe(gulp.dest(FIREFOX_BUILD_CONTENT_DIR)),
+
     preprocessJS(FIREFOX_CONTENT_DIR + 'PdfStreamConverter.jsm', defines, true)
         .pipe(replace(/\bPDFJSSCRIPT_STREAM_CONVERTER_ID\b/g,
                       FIREFOX_STREAM_CONVERTER_ID))
@@ -860,6 +879,10 @@ gulp.task('mozcentral-pre', ['buildnumber', 'locale'], function () {
         .pipe(gulp.dest(MOZCENTRAL_EXTENSION_DIR)),
     gulp.src('LICENSE').pipe(gulp.dest(MOZCENTRAL_EXTENSION_DIR)),
 
+    gulp.src(FIREFOX_CONTENT_DIR + 'PdfJsDefaultPreferences.jsm')
+        .pipe(transform('utf8', preprocessDefaultPreferences))
+        .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
+
     preprocessJS(FIREFOX_CONTENT_DIR + 'PdfJs.jsm', defines, true)
         .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
     preprocessJS(FIREFOX_CONTENT_DIR + 'PdfStreamConverter.jsm', defines, true)