diff --git a/src/library_browser.js b/src/library_browser.js
index ccd7de3310b7b..b7b1901be3130 100644
--- a/src/library_browser.js
+++ b/src/library_browser.js
@@ -22,6 +22,7 @@ var LibraryBrowser = {
       arg: 0, // The argument that will be passed to the main loop. (of type void*)
       timingMode: 0,
       timingValue: 0,
+      timingInitialized: 0,
       currentFrameNumber: 0,
       queue: [],
       pause: function() {
@@ -1037,6 +1038,9 @@ var LibraryBrowser = {
 
   // Runs natively in pthread, no __proxy needed.
   emscripten_set_main_loop_timing: function(mode, value) {
+    if (Browser.mainLoop.timingInitialized) {
+      return 1;
+    }
     Browser.mainLoop.timingMode = mode;
     Browser.mainLoop.timingValue = value;
 
@@ -1086,6 +1090,7 @@ var LibraryBrowser = {
       };
       Browser.mainLoop.method = 'immediate';
     }
+    Browser.mainLoop.timingInitialized = 1;
     return 0;
   },
 
diff --git a/src/library_html5.js b/src/library_html5.js
index 9509a7280e42c..ba897614bcd27 100644
--- a/src/library_html5.js
+++ b/src/library_html5.js
@@ -47,6 +47,7 @@ var LibraryJSEvents = {
           JSEvents.numGamepadsConnected = firstState.length;
         }
       }
+      Module['processWindowSelectorChange'] = JSEvents.processWindowSelectorChange;
     },
 
     registerRemoveEventListeners: function() {
@@ -145,6 +146,7 @@ var LibraryJSEvents = {
 
     // Stores objects representing each currently registered JS event handler.
     eventHandlers: [],
+    windowSelectorChangeHandler: 0,
 
     isInternetExplorer: function() { return navigator.userAgent.indexOf('MSIE') !== -1 || navigator.appVersion.indexOf('Trident/') > 0; },
 
@@ -710,6 +712,15 @@ var LibraryJSEvents = {
       return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
     },
 
+    processWindowSelectorChange: function() {
+      if (JSEvents.windowSelectorChangeHandler) {
+        Module.dynCall_v(JSEvents.windowSelectorChangeHandler);
+      }
+      if (GLctx) {
+        GLctx["clear"](GLctx["COLOR_BUFFER_BIT"] | GLctx["DEPTH_BUFFER_BIT"] | GLctx["STENCIL_BUFFER_BIT"]);
+      }
+    },
+
     fillPointerlockChangeEventData: function(eventStruct, e) {
       var pointerLockElement = document.pointerLockElement || document.mozPointerLockElement || document.webkitPointerLockElement || document.msPointerLockElement;
       var isPointerlocked = !!pointerLockElement;
@@ -1945,6 +1956,100 @@ var LibraryJSEvents = {
     return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
   },
 
+  _emscripten_get_window_index_by_data: function(selector, data) {
+    for (var i = 0; i < selector.options.length; ++i) {
+      if (selector.options[i].value == data) {
+        return i;
+      }
+    }
+    return -1;
+  },
+
+  emscripten_add_window__deps: ['_emscripten_get_window_index_by_data', '$JSEvents'],
+  emscripten_add_window: function(title, data) {
+    var selector = JSEvents.findEventTarget('windowSelector');
+    if (!selector) {
+      return {{{ cDefine('EMSCRIPTEN_RESULT_NOT_SUPPORTED') }}};
+    }
+    if (__emscripten_get_window_index_by_data(selector, data) != -1) {
+      return {{{ cDefine('EMSCRIPTEN_RESULT_INVALID_PARAM') }}};
+    }
+    var newWindowOption = document.createElement('option');
+    newWindowOption.value = data;
+    newWindowOption.text = UTF8ToString(title);
+    selector.add(newWindowOption);
+    if (selector.options.length == 1) {
+      selector.selectedIndex = 0;
+    }
+    if (selector.options.length > 1) {
+      selector.hidden = false;
+    }
+    Module.processWindowSelectorChange();
+    return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
+  },
+
+  _emscripten_modify_window__deps: ['_emscripten_get_window_index_by_data', '$JSEvents'],
+  _emscripten_modify_window: function(data, func) {
+    var selector = JSEvents.findEventTarget('windowSelector');
+    if (!selector) {
+      return {{{ cDefine('EMSCRIPTEN_RESULT_NOT_SUPPORTED') }}};
+    }
+    var ind = __emscripten_get_window_index_by_data(selector, data);
+    if (ind != -1) {
+      return func(selector, ind);
+    } else {
+      return {{{ cDefine('EMSCRIPTEN_RESULT_NO_DATA') }}};
+    }
+  },
+
+  emscripten_set_window_title__deps: ['_emscripten_modify_window'],
+  emscripten_set_window_title: function(title, data) {
+    __emscripten_modify_window(data, function(selector, ind) {
+      if (title) {
+        selector.options[ind].text = UTF8ToString(title);
+        return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
+      } else {
+        return {{{ cDefine('EMSCRIPTEN_RESULT_INVALID_PARAM') }}};
+      }
+    });
+  },
+
+  emscripten_remove_window__deps: ['_emscripten_modify_window'],
+  emscripten_remove_window: function(data) {
+    __emscripten_modify_window(data, function(selector, ind) {
+      selector.remove(ind);
+      Module.processWindowSelectorChange();
+      return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
+    });
+  },
+
+  emscripten_get_current_window_data__deps: ['$JSEvents'],
+  emscripten_get_current_window_data: function() {
+    var selector = JSEvents.findEventTarget('windowSelector');
+    if (!selector) {
+      return 0;
+    }
+    var ind = selector.selectedIndex;
+    if (ind < 0) {
+      return 0;
+    }
+    return selector.options[ind].value | 0;
+  },
+
+  emscripten_set_current_window__deps: ['_emscripten_modify_window'],
+  emscripten_set_current_window: function(data) {
+    __emscripten_modify_window(data, function(selector, ind) {
+      selector.selectedIndex = ind;
+      Module.processWindowSelectorChange();
+      return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
+    });
+  },
+
+  emscripten_set_selected_window_change_callback__deps: ['$JSEvents'],
+  emscripten_set_selected_window_change_callback: function(func) {
+    JSEvents.windowSelectorChangeHandler = func;
+  },
+
   emscripten_set_element_css_size: function(target, width, height) {
     if (!target) {
       target = Module['canvas'];
diff --git a/src/shell.html b/src/shell.html
index 7b494f1a7f034..1c7e2452cc4fe 100644
--- a/src/shell.html
+++ b/src/shell.html
@@ -1199,6 +1199,7 @@
     <div class="emscripten" id="status">Downloading...</div>
 
 <span id='controls'>
+  <span><select id="windowSelector" hidden="true" onchange="Module.processWindowSelectorChange()"/></span>
   <span><input type="checkbox" id="resize">Resize canvas</span>
   <span><input type="checkbox" id="pointerLock" checked>Lock/hide mouse pointer &nbsp;&nbsp;&nbsp;</span>
   <span><input type="button" value="Fullscreen" onclick="Module.requestFullscreen(document.getElementById('pointerLock').checked, 
diff --git a/system/include/emscripten/html5.h b/system/include/emscripten/html5.h
index faccfd41234de..86f047669b6f7 100644
--- a/system/include/emscripten/html5.h
+++ b/system/include/emscripten/html5.h
@@ -441,6 +441,14 @@ extern EMSCRIPTEN_RESULT emscripten_webgl_commit_frame();
 extern EMSCRIPTEN_RESULT emscripten_set_canvas_element_size(const char *target, int width, int height);
 extern EMSCRIPTEN_RESULT emscripten_get_canvas_element_size(const char *target, int *width, int *height);
 
+#define EMSCRIPTEN_HAS_WINDOW_SELECTOR
+extern EMSCRIPTEN_RESULT emscripten_add_window(const char *title, void *data);
+extern EMSCRIPTEN_RESULT emscripten_set_window_title(const char *title, void *data);
+extern EMSCRIPTEN_RESULT emscripten_remove_window(void *data);
+extern void *emscripten_get_current_window_data(void);
+extern EMSCRIPTEN_RESULT emscripten_set_current_window(void *data);
+extern EMSCRIPTEN_RESULT emscripten_set_selected_window_change_callback(void (*func)(void));
+
 extern EMSCRIPTEN_RESULT emscripten_set_element_css_size(const char *target, double width, double height);
 extern EMSCRIPTEN_RESULT emscripten_get_element_css_size(const char *target, double *width, double *height);