diff --git a/src/display/api.js b/src/display/api.js
index 6e8abb6e9..d3d6b0b89 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -65,7 +65,8 @@ const RENDERING_CANCELLED_TIMEOUT = 100; // ms
  * @typedef {function} IPDFStreamFactory
  * @param {DocumentInitParameters} params - The document initialization
  *   parameters. The "url" key is always present.
- * @returns {IPDFStream}
+ * @returns {Promise} A promise, which is resolved with an instance of
+ *   {IPDFStream}.
  * @ignore
  */
 
@@ -80,7 +81,7 @@ let createPDFNetworkStream;
  * data transport.
  * @param {IPDFStreamFactory} pdfNetworkStreamFactory - The factory function
  *   that takes document initialization parameters (including a "url") and
- *   returns an instance of {IPDFStream}.
+ *   returns a promise which is resolved with an instance of {IPDFStream}.
  * @ignore
  */
 function setPDFNetworkStreamFactory(pdfNetworkStreamFactory) {
@@ -313,34 +314,44 @@ function getDocument(src) {
       if (task.destroyed) {
         throw new Error("Loading aborted");
       }
-      return _fetchDocument(worker, params, rangeTransport, docId).then(
-        function (workerId) {
-          if (task.destroyed) {
-            throw new Error("Loading aborted");
-          }
 
-          let networkStream;
-          if (rangeTransport) {
-            networkStream = new PDFDataTransportStream(
-              {
-                length: params.length,
-                initialData: params.initialData,
-                progressiveDone: params.progressiveDone,
-                disableRange: params.disableRange,
-                disableStream: params.disableStream,
-              },
-              rangeTransport
-            );
-          } else if (!params.data) {
-            networkStream = createPDFNetworkStream({
-              url: params.url,
+      const workerIdPromise = _fetchDocument(
+        worker,
+        params,
+        rangeTransport,
+        docId
+      );
+      const networkStreamPromise = new Promise(function (resolve) {
+        let networkStream;
+        if (rangeTransport) {
+          networkStream = new PDFDataTransportStream(
+            {
               length: params.length,
-              httpHeaders: params.httpHeaders,
-              withCredentials: params.withCredentials,
-              rangeChunkSize: params.rangeChunkSize,
+              initialData: params.initialData,
+              progressiveDone: params.progressiveDone,
               disableRange: params.disableRange,
               disableStream: params.disableStream,
-            });
+            },
+            rangeTransport
+          );
+        } else if (!params.data) {
+          networkStream = createPDFNetworkStream({
+            url: params.url,
+            length: params.length,
+            httpHeaders: params.httpHeaders,
+            withCredentials: params.withCredentials,
+            rangeChunkSize: params.rangeChunkSize,
+            disableRange: params.disableRange,
+            disableStream: params.disableStream,
+          });
+        }
+        resolve(networkStream);
+      });
+
+      return Promise.all([workerIdPromise, networkStreamPromise]).then(
+        function ([workerId, networkStream]) {
+          if (task.destroyed) {
+            throw new Error("Loading aborted");
           }
 
           const messageHandler = new MessageHandler(
diff --git a/src/display/fetch_stream.js b/src/display/fetch_stream.js
index c74483025..a1b9c9023 100644
--- a/src/display/fetch_stream.js
+++ b/src/display/fetch_stream.js
@@ -26,6 +26,12 @@ import {
   validateResponseStatus,
 } from "./network_utils.js";
 
+if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
+  throw new Error(
+    'Module "./fetch_stream.js" shall not be used with MOZCENTRAL builds.'
+  );
+}
+
 function createFetchOptions(headers, withCredentials, abortController) {
   return {
     method: "GET",
diff --git a/src/display/node_stream.js b/src/display/node_stream.js
index 79125524a..bbfb5b844 100644
--- a/src/display/node_stream.js
+++ b/src/display/node_stream.js
@@ -14,11 +14,6 @@
  */
 /* globals __non_webpack_require__ */
 
-const fs = __non_webpack_require__("fs");
-const http = __non_webpack_require__("http");
-const https = __non_webpack_require__("https");
-const url = __non_webpack_require__("url");
-
 import {
   AbortException,
   assert,
@@ -30,6 +25,17 @@ import {
   validateRangeRequestCapabilities,
 } from "./network_utils.js";
 
+if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
+  throw new Error(
+    'Module "./node_stream.js" shall not be used with MOZCENTRAL builds.'
+  );
+}
+
+const fs = __non_webpack_require__("fs");
+const http = __non_webpack_require__("http");
+const https = __non_webpack_require__("https");
+const url = __non_webpack_require__("url");
+
 const fileUriRegex = /^file:\/\/\/[a-zA-Z]:\//;
 
 function parseUrl(sourceUrl) {
diff --git a/src/pdf.js b/src/pdf.js
index 2233f3438..3e3c2d018 100644
--- a/src/pdf.js
+++ b/src/pdf.js
@@ -30,7 +30,24 @@ var pdfjsDisplaySVG = require("./display/svg.js");
 const pdfjsDisplayWorkerOptions = require("./display/worker_options.js");
 const pdfjsDisplayAPICompatibility = require("./display/api_compatibility.js");
 
-if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
+if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")) {
+  const streamsPromise = Promise.all([
+    SystemJS.import("pdfjs/display/network.js"),
+    SystemJS.import("pdfjs/display/fetch_stream.js"),
+  ]);
+  pdfjsDisplayAPI.setPDFNetworkStreamFactory(params => {
+    return streamsPromise.then(streams => {
+      const [{ PDFNetworkStream }, { PDFFetchStream }] = streams;
+      if (
+        pdfjsDisplayDisplayUtils.isFetchSupported() &&
+        pdfjsDisplayDisplayUtils.isValidFetchUrl(params.url)
+      ) {
+        return new PDFFetchStream(params);
+      }
+      return new PDFNetworkStream(params);
+    });
+  });
+} else if (PDFJSDev.test("GENERIC")) {
   const { isNodeJS } = require("./shared/is_node.js");
   if (isNodeJS) {
     const PDFNodeStream = require("./display/node_stream.js").PDFNodeStream;