diff --git a/examples/browserify/main.js b/examples/browserify/main.js
index 46a921a59..42c640ef0 100644
--- a/examples/browserify/main.js
+++ b/examples/browserify/main.js
@@ -10,9 +10,6 @@ var pdfPath = '../helloworld/helloworld.pdf';
 // Setting worker path to worker bundle.
 PDFJS.workerSrc = '../../build/browserify/pdf.worker.bundle.js';
 
-// It is also possible to disable workers via `PDFJS.disableWorker = true`,
-// however that might degrade the UI performance in web browsers.
-
 // Loading a document.
 var loadingTask = PDFJS.getDocument(pdfPath);
 loadingTask.promise.then(function (pdfDocument) {
diff --git a/examples/learning/helloworld.html b/examples/learning/helloworld.html
index 4142ef6f5..c2988c287 100644
--- a/examples/learning/helloworld.html
+++ b/examples/learning/helloworld.html
@@ -19,13 +19,6 @@
   //
   var url = './helloworld.pdf';
 
-  //
-  // Disable workers to avoid yet another cross-origin issue (workers need
-  // the URL of the script to be loaded, and dynamically loading a cross-origin
-  // script does not work).
-  //
-  // PDFJS.disableWorker = true;
-
   //
   // The workerSrc property shall be specified.
   //
diff --git a/examples/learning/helloworld64.html b/examples/learning/helloworld64.html
index 58890fe87..69420495a 100644
--- a/examples/learning/helloworld64.html
+++ b/examples/learning/helloworld64.html
@@ -31,12 +31,6 @@
     'MDAwIG4gCjAwMDAwMDAzODAgMDAwMDAgbiAKdHJhaWxlcgo8PAogIC9TaXplIDYKICAvUm9v' +
     'dCAxIDAgUgo+PgpzdGFydHhyZWYKNDkyCiUlRU9G');
 
-  // Disable workers to avoid yet another cross-origin issue (workers need
-  // the URL of the script to be loaded, and dynamically loading a cross-origin
-  // script does not work).
-  //
-  // PDFJS.disableWorker = true;
-
   //
   // The workerSrc property shall be specified.
   //
diff --git a/examples/learning/prevnext.html b/examples/learning/prevnext.html
index 463527a3d..f7e68f2b5 100644
--- a/examples/learning/prevnext.html
+++ b/examples/learning/prevnext.html
@@ -28,14 +28,6 @@
   //
   var url = '../../web/compressed.tracemonkey-pldi-09.pdf';
 
-
-  //
-  // Disable workers to avoid yet another cross-origin issue (workers need
-  // the URL of the script to be loaded, and dynamically loading a cross-origin
-  // script does not work).
-  //
-  // PDFJS.disableWorker = true;
-
   //
   // In cases when the pdf.worker.js is located at the different folder than the
   // pdf.js's one, or the pdf.js is executed via eval(), the workerSrc property
diff --git a/examples/webpack/main.js b/examples/webpack/main.js
index d0466b86d..d1beb101c 100644
--- a/examples/webpack/main.js
+++ b/examples/webpack/main.js
@@ -10,9 +10,6 @@ var pdfPath = '../helloworld/helloworld.pdf';
 // Setting worker path to worker bundle.
 pdfjsLib.PDFJS.workerSrc = '../../build/webpack/pdf.worker.bundle.js';
 
-// It is also possible to disable workers via `PDFJS.disableWorker = true`,
-// however that might degrade the UI performance in web browsers.
-
 // Loading a document.
 var loadingTask = pdfjsLib.getDocument(pdfPath);
 loadingTask.promise.then(function (pdfDocument) {
diff --git a/external/dist/webpack.js b/external/dist/webpack.js
index f2c4a6400..af3979439 100644
--- a/external/dist/webpack.js
+++ b/external/dist/webpack.js
@@ -19,8 +19,6 @@ var PdfjsWorker = require('worker-loader!./build/pdf.worker.js');
 
 if (typeof window !== 'undefined' && 'Worker' in window) {
   pdfjs.PDFJS.workerPort = new PdfjsWorker();
-} else {
-  pdfjs.PDFJS.disableWorker = true;
 }
 
 module.exports = pdfjs;
diff --git a/src/display/api.js b/src/display/api.js
index afc08c047..c62c3e7c1 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -1216,6 +1216,19 @@ var PDFWorker = (function PDFWorkerClosure() {
     throw new Error('No PDFJS.workerSrc specified');
   }
 
+  function getMainThreadWorkerMessageHandler() {
+    if (typeof window === 'undefined') {
+      return null;
+    }
+    if (typeof PDFJSDev === 'undefined' || !PDFJSDev.test('PRODUCTION')) {
+      return (window.pdfjsNonProductionPdfWorker &&
+              window.pdfjsNonProductionPdfWorker.WorkerMessageHandler);
+    }
+    // PRODUCTION
+    return (window.pdfjsDistBuildPdfWorker &&
+            window.pdfjsDistBuildPdfWorker.WorkerMessageHandler);
+  }
+
   let fakeWorkerFilesLoadedCapability;
 
   // Loads worker code into main thread.
@@ -1225,6 +1238,13 @@ var PDFWorker = (function PDFWorkerClosure() {
       return fakeWorkerFilesLoadedCapability.promise;
     }
     fakeWorkerFilesLoadedCapability = createPromiseCapability();
+
+    let mainWorkerMessageHandler = getMainThreadWorkerMessageHandler();
+    if (mainWorkerMessageHandler) {
+      // The worker was already loaded using a `<script>` tag.
+      fakeWorkerFilesLoadedCapability.resolve(mainWorkerMessageHandler);
+      return fakeWorkerFilesLoadedCapability.promise;
+    }
     // In the developer build load worker_loader which in turn loads all the
     // other files and resolves the promise. In production only the
     // pdf.worker.js file is needed.
@@ -1316,7 +1336,7 @@ var PDFWorker = (function PDFWorkerClosure() {
       // Right now, the requirement is, that an Uint8Array is still an
       // Uint8Array as it arrives on the worker. (Chrome added this with v.15.)
       if (typeof Worker !== 'undefined' && !isWorkerDisabled &&
-          !getDefaultSetting('disableWorker')) {
+          !getMainThreadWorkerMessageHandler()) {
         var workerSrc = getWorkerSrc();
 
         try {
@@ -1427,7 +1447,7 @@ var PDFWorker = (function PDFWorkerClosure() {
     },
 
     _setupFakeWorker: function PDFWorker_setupFakeWorker() {
-      if (!isWorkerDisabled && !getDefaultSetting('disableWorker')) {
+      if (!isWorkerDisabled) {
         warn('Setting up fake worker.');
         isWorkerDisabled = true;
       }
diff --git a/src/display/dom_utils.js b/src/display/dom_utils.js
index 442d163e0..e8c0d28a9 100644
--- a/src/display/dom_utils.js
+++ b/src/display/dom_utils.js
@@ -361,8 +361,6 @@ function getDefaultSetting(id) {
       return globalSettings ? globalSettings.workerPort : null;
     case 'workerSrc':
       return globalSettings ? globalSettings.workerSrc : null;
-    case 'disableWorker':
-      return globalSettings ? globalSettings.disableWorker : false;
     case 'maxImageSize':
       return globalSettings ? globalSettings.maxImageSize : -1;
     case 'imageResourcesPath':
diff --git a/src/display/global.js b/src/display/global.js
index 885781cd6..b6be09482 100644
--- a/src/display/global.js
+++ b/src/display/global.js
@@ -128,15 +128,6 @@ PDFJS.disableFontFace = (PDFJS.disableFontFace === undefined ?
 PDFJS.imageResourcesPath = (PDFJS.imageResourcesPath === undefined ?
                             '' : PDFJS.imageResourcesPath);
 
-/**
- * Disable the web worker and run all code on the main thread. This will
- * happen automatically if the browser doesn't support workers or sending
- * typed arrays to workers.
- * @var {boolean}
- */
-PDFJS.disableWorker = (PDFJS.disableWorker === undefined ?
-                       false : PDFJS.disableWorker);
-
 /**
  * Path and filename of the worker file. Required when the worker is enabled
  * in development mode. If unspecified in the production build, the worker
@@ -148,8 +139,7 @@ PDFJS.disableWorker = (PDFJS.disableWorker === undefined ?
 PDFJS.workerSrc = (PDFJS.workerSrc === undefined ? null : PDFJS.workerSrc);
 
 /**
- * Defines global port for worker process. Overrides workerSrc and
- * disableWorker setting.
+ * Defines global port for worker process. Overrides `workerSrc` setting.
  */
 PDFJS.workerPort = (PDFJS.workerPort === undefined ? null : PDFJS.workerPort);
 
diff --git a/test/unit/api_spec.js b/test/unit/api_spec.js
index 955200eff..12252e079 100644
--- a/test/unit/api_spec.js
+++ b/test/unit/api_spec.js
@@ -122,16 +122,14 @@ describe('api', function() {
             path: TEST_PDFS_PATH.node + basicApiFileName,
           });
         } else {
-          var nonBinaryRequest = PDFJS.disableWorker;
-          var request = new XMLHttpRequest();
+          let nonBinaryRequest = false;
+          let request = new XMLHttpRequest();
           request.open('GET', TEST_PDFS_PATH.dom + basicApiFileName, false);
-          if (!nonBinaryRequest) {
-            try {
-              request.responseType = 'arraybuffer';
-              nonBinaryRequest = request.responseType !== 'arraybuffer';
-            } catch (e) {
-              nonBinaryRequest = true;
-            }
+          try {
+            request.responseType = 'arraybuffer';
+            nonBinaryRequest = request.responseType !== 'arraybuffer';
+          } catch (e) {
+            nonBinaryRequest = true;
           }
           if (nonBinaryRequest && request.overrideMimeType) {
             request.overrideMimeType('text/plain; charset=x-user-defined');
diff --git a/web/app.js b/web/app.js
index edeea6ec3..3bfa7e893 100644
--- a/web/app.js
+++ b/web/app.js
@@ -22,8 +22,8 @@ import {
 } from './ui_utils';
 import {
   build, createBlob, getDocument, getFilenameFromUrl, InvalidPDFException,
-  MissingPDFException, OPS, PDFJS, shadow, UnexpectedResponseException,
-  UNSUPPORTED_FEATURES, version
+  MissingPDFException, OPS, PDFJS, PDFWorker, shadow,
+  UnexpectedResponseException, UNSUPPORTED_FEATURES, version
 } from 'pdfjs-lib';
 import { CursorTool, PDFCursorTools } from './pdf_cursor_tools';
 import { PDFRenderingQueue, RenderingStates } from './pdf_rendering_queue';
@@ -285,8 +285,9 @@ let PDFViewerApplication = {
       let hash = document.location.hash.substring(1);
       let hashParams = parseQueryString(hash);
 
-      if ('disableworker' in hashParams) {
-        PDFJS.disableWorker = (hashParams['disableworker'] === 'true');
+      if ('disableworker' in hashParams &&
+          hashParams['disableworker'] === 'true') {
+        waitOn.push(loadFakeWorker());
       }
       if ('disablerange' in hashParams) {
         PDFJS.disableRange = (hashParams['disablerange'] === 'true');
@@ -1512,6 +1513,35 @@ if (typeof PDFJSDev === 'undefined' || PDFJSDev.test('GENERIC')) {
   };
 }
 
+function loadFakeWorker() {
+  return new Promise(function(resolve, reject) {
+    if (typeof PDFJSDev === 'undefined' || !PDFJSDev.test('PRODUCTION')) {
+      if (typeof SystemJS === 'object') {
+        SystemJS.import('pdfjs/core/worker').then((worker) => {
+          window.pdfjsNonProductionPdfWorker = worker;
+          resolve();
+        });
+      } else if (typeof require === 'function') {
+        window.pdfjsNonProductionPdfWorker = require('../src/core/worker.js');
+        resolve();
+      } else {
+        reject(new Error(
+          'SystemJS or CommonJS must be used to load fake worker.'));
+      }
+    } else {
+      let script = document.createElement('script');
+      script.src = PDFWorker.getWorkerSrc();
+      script.onload = function() {
+        resolve();
+      };
+      script.onerror = function() {
+        reject(new Error(`Cannot load fake worker at: ${script.src}`));
+      };
+      (document.head || document.documentElement).appendChild(script);
+    }
+  });
+}
+
 function loadAndEnablePDFBug(enabledTabs) {
   return new Promise(function (resolve, reject) {
     let appConfig = PDFViewerApplication.appConfig;