diff --git a/caps/nsPrincipal.cpp b/caps/nsPrincipal.cpp
index 492cb674aed1..60885ab548b1 100644
--- a/caps/nsPrincipal.cpp
+++ b/caps/nsPrincipal.cpp
@@ -31,7 +31,6 @@
 #include "mozilla/HashFunctions.h"
 
 #include "nsIAppsService.h"
-#include "mozIApplication.h"
 
 using namespace mozilla;
 
diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index 8d5fdd98845a..3a736518caba 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -43,7 +43,6 @@
 #include "nsIDOMStorage.h"
 #include "nsIContentViewer.h"
 #include "nsIDocumentLoaderFactory.h"
-#include "nsIMozBrowserFrame.h"
 #include "nsCURILoader.h"
 #include "nsDocShellCID.h"
 #include "nsDOMCID.h"
@@ -10774,35 +10773,6 @@ nsDocShell::DoURILoad(nsIURI* aURI,
     "DoURILoad thinks this is a document and InternalLoad does not");
   }
 
-
-  // For mozWidget, display a load error if we navigate to a page which is not
-  // claimed in |widgetPages|.
-  // When we go to display a load error for an invalid mozWidget page, we will
-  // try to load an about:neterror page, which is also an invalid mozWidget
-  // page. To avoid recursion, we skip this check if aURI's scheme is "about".
-
-  // The goal is to prevent leaking sensitive information of an invalid page of
-  // an app, so allowing about:blank would not be conflict to the goal.
-  bool isAbout = false;
-  rv = aURI->SchemeIs("about", &isAbout);
-  if (NS_SUCCEEDED(rv) && !isAbout &&
-      nsIDocShell::GetIsApp()) {
-    nsCOMPtr<Element> frameElement = mScriptGlobal->AsOuter()->GetFrameElementInternal();
-    if (frameElement) {
-      nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(frameElement);
-      // |GetReallyIsApp| indicates the browser frame is a valid app or widget.
-      // Here we prevent navigating to an app or widget which loses its validity
-      // by loading invalid page or other way.
-      if (browserFrame && !browserFrame->GetReallyIsApp()) {
-        nsCOMPtr<nsIObserverService> serv = services::GetObserverService();
-        if (serv) {
-            serv->NotifyObservers(GetDocument(), "invalid-widget", nullptr);
-        }
-        return NS_ERROR_MALFORMED_URI;
-      }
-    }
-  }
-
   // open a channel for the url
   nsCOMPtr<nsIChannel> channel;
 
diff --git a/dom/apps/AppsUtils.jsm b/dom/apps/AppsUtils.jsm
index 73e58e5bebd2..6df9bbc84a0e 100644
--- a/dom/apps/AppsUtils.jsm
+++ b/dom/apps/AppsUtils.jsm
@@ -53,15 +53,6 @@ mozIApplication.prototype = {
     return (perm === Ci.nsIPermissionManager.ALLOW_ACTION);
   },
 
-  hasWidgetPage: function(aPageURL) {
-    let uri = Services.io.newURI(aPageURL, null, null);
-    let filepath = AppsUtils.getFilePath(uri.path);
-    let eliminatedUri = Services.io.newURI(uri.prePath + filepath, null, null);
-    let equalCriterion = aUrl => Services.io.newURI(aUrl, null, null)
-                                            .equals(eliminatedUri);
-    return this.widgetPages.find(equalCriterion) !== undefined;
-  },
-
   get principal() {
     if (this._principal) {
       return this._principal;
@@ -122,7 +113,6 @@ function _setAppProperties(aObj, aApp) {
   aObj.storeId = aApp.storeId || "";
   aObj.storeVersion = aApp.storeVersion || 0;
   aObj.role = aApp.role || "";
-  aObj.widgetPages = aApp.widgetPages || [];
   aObj.kind = aApp.kind;
   aObj.enabled = aApp.enabled !== undefined ? aApp.enabled : true;
   aObj.sideloaded = aApp.sideloaded;
@@ -854,10 +844,6 @@ ManifestHelper.prototype = {
     return this._localeProp("package_path");
   },
 
-  get widgetPages() {
-    return this._localeProp("widgetPages");
-  },
-
   get size() {
     return this._manifest["size"] || 0;
   },
diff --git a/dom/apps/PermissionsTable.jsm b/dom/apps/PermissionsTable.jsm
index 13bd21871db8..8430c76567ed 100644
--- a/dom/apps/PermissionsTable.jsm
+++ b/dom/apps/PermissionsTable.jsm
@@ -268,11 +268,6 @@ this.PermissionsTable =  { geolocation: {
                              privileged: DENY_ACTION,
                              certified: ALLOW_ACTION
                            },
-                           "embed-widgets": {
-                             app: DENY_ACTION,
-                             privileged: ALLOW_ACTION,
-                             certified: ALLOW_ACTION
-                           },
                            "background-sensors": {
                              app: DENY_ACTION,
                              privileged: DENY_ACTION,
diff --git a/dom/apps/tests/unit/test_has_widget_criterion.js b/dom/apps/tests/unit/test_has_widget_criterion.js
deleted file mode 100644
index 31ef90e90630..000000000000
--- a/dom/apps/tests/unit/test_has_widget_criterion.js
+++ /dev/null
@@ -1,66 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-var {classes: Cc, interfaces: Ci, utils: Cu} = Components;
-
-Cu.import("resource:///modules/AppsUtils.jsm");
-Cu.import("resource:///modules/Services.jsm");
-
-add_test(function test_has_widget_criterion() {
-
-  // follow the logic |_saveWidgetsFullPath|
-  let baseUri = Services.io.newURI('http://example.com', null, null);
-  let resolve = (aPage)=>{
-    let filepath = AppsUtils.getFilePath(aPage);
-
-    return baseUri.resolve(filepath);
-  };
-
-  let widgetPages = ['/widget.html',
-                     '/foo/bar.html'];
-  let resolvedWidgetPages = widgetPages.map(resolve);
-
-  let app = new mozIApplication({widgetPages:resolvedWidgetPages});
-
-  let widgetPageCheck = aPage => app.hasWidgetPage(baseUri.resolve(aPage));
-
-  Assert.ok(widgetPageCheck('/widget.html'), 'should pass for identical path');
-  Assert.ok(widgetPageCheck('/foo/bar.html'), 'should pass for identical path');
-
-  Assert.ok(!widgetPageCheck('/wrong.html'), 'should not pass for wrong path');
-  Assert.ok(!widgetPageCheck('/WIDGET.html'), 'should be case _sensitive_ for path');
-  Assert.ok(!widgetPageCheck('/widget.HTML'), 'should be case _sensitive_ for file extension');
-
-  Assert.ok(widgetPageCheck('/widget.html?aQuery'), 'should be query insensitive');
-  Assert.ok(widgetPageCheck('/widget.html#aHash'), 'should be hash insensitive');
-  Assert.ok(widgetPageCheck('/widget.html?aQuery=aquery#aHash'),
-                            'should be hash/query insensitive');
-
-  Assert.ok(widgetPageCheck('HTTP://example.com/widget.html'),
-                            'should be case insensitive for protocol');
-  Assert.ok(widgetPageCheck('http://EXAMPLE.COM/widget.html'),
-                            'should be case insensitive for domain');
-  Assert.ok(widgetPageCheck('http://example.com:80/widget.html'),
-                            'should pass for default port');
-
-  Assert.ok(widgetPageCheck('HTTP://EXAMPLE.COM:80/widget.html?QueryA=queryA&QueryB=queryB#aHash'),
-                            'should pass for a really mess one');
-
-  Assert.ok(!widgetPageCheck('foo://example.com/widget.html'),
-                            'should not pass for wrong protocol');
-  Assert.ok(!widgetPageCheck('https://example.com/widget.html'),
-                            'should not pass for wrong protocol');
-  Assert.ok(!widgetPageCheck('/wrong/widget.html'),
-                            'should not pass for additional path');
-  Assert.ok(!widgetPageCheck('/bar.html'),
-                            'should not pass for reduced path');
-  Assert.ok(!widgetPageCheck('http://username:password@example.com/widget.html'),
-                            'should not pass for userinfo');
-  Assert.ok(!widgetPageCheck('http://example.com:8080/widget.html'),
-                             'should not pass non-default port');
-  run_next_test();
-});
-
-function run_test() {
-  run_next_test();
-}
diff --git a/dom/apps/tests/unit/xpcshell.ini b/dom/apps/tests/unit/xpcshell.ini
index aa2af155cae4..9745b198f254 100644
--- a/dom/apps/tests/unit/xpcshell.ini
+++ b/dom/apps/tests/unit/xpcshell.ini
@@ -1,6 +1,5 @@
 [DEFAULT]
 
-[test_has_widget_criterion.js]
 [test_manifestSanitizer.js]
 [test_manifestHelper.js]
 [test_moziapplication.js]
diff --git a/dom/base/nsFrameLoader.cpp b/dom/base/nsFrameLoader.cpp
index 307a78e60308..b1a44e7905fe 100644
--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -1765,22 +1765,6 @@ nsFrameLoader::GetOwnerIsMozBrowserOrAppFrame(bool* aResult)
   return NS_OK;
 }
 
-bool
-nsFrameLoader::OwnerIsWidget()
-{
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
-  return browserFrame ? browserFrame->GetReallyIsWidget() : false;
-}
-
-
-// The xpcom getter version
-NS_IMETHODIMP
-nsFrameLoader::GetOwnerIsWidget(bool* aResult)
-{
-  *aResult = OwnerIsWidget();
-  return NS_OK;
-}
-
 bool
 nsFrameLoader::OwnerIsAppFrame()
 {
diff --git a/dom/base/nsFrameLoader.h b/dom/base/nsFrameLoader.h
index fb820d734e52..6f9f14548e08 100644
--- a/dom/base/nsFrameLoader.h
+++ b/dom/base/nsFrameLoader.h
@@ -248,12 +248,6 @@ private:
    */
   bool OwnerIsMozBrowserOrAppFrame();
 
-  /**
-   * Is this a frameloader for a bona fide <iframe mozwidget>?  (I.e., does the
-   * frame return true for nsIMozBrowserFrame::GetReallyIsWidget()?)
-   */
-  bool OwnerIsWidget();
-
   /**
    * Is this a frameloader for a bona fide <iframe mozapp>?  (I.e., does the
    * frame return true for nsIMozBrowserFrame::GetReallyIsApp()?)
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index 7253653efcfd..9a22e161b56d 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -102,7 +102,6 @@ GK_ATOM(anonid, "anonid")
 GK_ATOM(anonlocation, "anonlocation")
 GK_ATOM(any, "any")
 GK_ATOM(mozapp, "mozapp")
-GK_ATOM(mozwidget, "mozwidget")
 GK_ATOM(applet, "applet")
 GK_ATOM(applyImports, "apply-imports")
 GK_ATOM(applyTemplates, "apply-templates")
diff --git a/dom/base/nsIFrameLoader.idl b/dom/base/nsIFrameLoader.idl
index c9e20bae1f2f..df210c1184d4 100644
--- a/dom/base/nsIFrameLoader.idl
+++ b/dom/base/nsIFrameLoader.idl
@@ -213,12 +213,6 @@ interface nsIFrameLoader : nsISupports
    */
   readonly attribute boolean ownerIsMozBrowserOrAppFrame;
 
-  /**
-   * Find out whether the owner content really is a widget. If this attribute
-   * returns true, |ownerIsMozBrowserOrAppFrame| must return true.
-   */
-  readonly attribute boolean ownerIsWidget;
-
   /**
    * The last known width of the frame. Reading this property will not trigger
    * a reflow, and therefore may not reflect the current state of things. It
diff --git a/dom/browser-element/BrowserElementChildPreload.js b/dom/browser-element/BrowserElementChildPreload.js
index 1332cc9a63f1..780dfa80e8ae 100644
--- a/dom/browser-element/BrowserElementChildPreload.js
+++ b/dom/browser-element/BrowserElementChildPreload.js
@@ -70,7 +70,6 @@ var OBSERVED_EVENTS = [
   'xpcom-shutdown',
   'audio-playback',
   'activity-done',
-  'invalid-widget',
   'will-launch-app'
 ];
 
@@ -397,9 +396,6 @@ BrowserElementChild.prototype = {
       case 'xpcom-shutdown':
         this._shuttingDown = true;
         break;
-      case 'invalid-widget':
-        sendAsyncMsg('error', { type: 'invalid-widget' });
-        break;
       case 'will-launch-app':
         // If the launcher is not visible, let's ignore the message.
         if (!docShell.isActive) {
diff --git a/dom/browser-element/BrowserElementParent.cpp b/dom/browser-element/BrowserElementParent.cpp
index cbd685f3d271..1edf125d6b9b 100644
--- a/dom/browser-element/BrowserElementParent.cpp
+++ b/dom/browser-element/BrowserElementParent.cpp
@@ -177,13 +177,6 @@ BrowserElementParent::DispatchOpenWindowEvent(Element* aOpenerFrameElement,
     return BrowserElementParent::OPEN_WINDOW_IGNORED;
   }
 
-  // Do not dispatch a mozbrowseropenwindow event of a widget to its embedder
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame =
-    do_QueryInterface(aOpenerFrameElement);
-  if (browserFrame && browserFrame->GetReallyIsWidget()) {
-    return BrowserElementParent::OPEN_WINDOW_CANCELLED;
-  }
-
   nsEventStatus status = nsEventStatus_eIgnore;
   bool dispatchSucceeded =
     DispatchCustomDOMEvent(aOpenerFrameElement,
diff --git a/dom/browser-element/BrowserElementParent.js b/dom/browser-element/BrowserElementParent.js
index 954c8293289b..450c1862381f 100644
--- a/dom/browser-element/BrowserElementParent.js
+++ b/dom/browser-element/BrowserElementParent.js
@@ -319,9 +319,6 @@ BrowserElementParent.prototype = {
 
   _setupMessageListener: function() {
     this._mm = this._frameLoader.messageManager;
-    this._isWidget = this._frameLoader
-                         .QueryInterface(Ci.nsIFrameLoader)
-                         .ownerIsWidget;
     this._mm.addMessageListener('browser-element-api:call', this);
     this._mm.loadFrameScript("chrome://global/content/extensions.js", true);
   },
@@ -389,7 +386,7 @@ BrowserElementParent.prototype = {
 
     if (aMsg.data.msg_name in mmCalls) {
       return mmCalls[aMsg.data.msg_name].apply(this, arguments);
-    } else if (!this._isWidget && aMsg.data.msg_name in mmSecuritySensitiveCalls) {
+    } else if (aMsg.data.msg_name in mmSecuritySensitiveCalls) {
       return mmSecuritySensitiveCalls[aMsg.data.msg_name].apply(this, arguments);
     }
   },
@@ -428,10 +425,8 @@ BrowserElementParent.prototype = {
       }
     };
 
-    // 1. We don't handle password-only prompts.
-    // 2. We don't handle for widget case because of security concern.
-    if (authDetail.isOnlyPassword ||
-        this._frameLoader.QueryInterface(Ci.nsIFrameLoader).ownerIsWidget) {
+    // We don't handle password-only prompts.
+    if (authDetail.isOnlyPassword) {
       cancelCallback();
       return;
     }
diff --git a/dom/html/nsBrowserElement.cpp b/dom/html/nsBrowserElement.cpp
index 0787cd11fd18..61ca3ca7924f 100644
--- a/dom/html/nsBrowserElement.cpp
+++ b/dom/html/nsBrowserElement.cpp
@@ -40,16 +40,6 @@ nsBrowserElement::IsBrowserElementOrThrow(ErrorResult& aRv)
   return false;
 }
 
-bool
-nsBrowserElement::IsNotWidgetOrThrow(ErrorResult& aRv)
-{
-  if (!mOwnerIsWidget) {
-    return true;
-  }
-  aRv.Throw(NS_ERROR_DOM_INVALID_NODE_TYPE_ERR);
-  return false;
-}
-
 void
 nsBrowserElement::InitBrowserElementAPI()
 {
@@ -58,8 +48,6 @@ nsBrowserElement::InitBrowserElementAPI()
   NS_ENSURE_TRUE_VOID(frameLoader);
   nsresult rv = frameLoader->GetOwnerIsMozBrowserOrAppFrame(&isMozBrowserOrApp);
   NS_ENSURE_SUCCESS_VOID(rv);
-  rv = frameLoader->GetOwnerIsWidget(&mOwnerIsWidget);
-  NS_ENSURE_SUCCESS_VOID(rv);
 
   if (!isMozBrowserOrApp) {
     return;
@@ -149,7 +137,6 @@ nsBrowserElement::SendMouseEvent(const nsAString& aType,
                                  ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->SendMouseEvent(aType,
                                                    aX,
@@ -177,7 +164,6 @@ nsBrowserElement::SendTouchEvent(const nsAString& aType,
                                  ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   if (aIdentifiers.Length() != aCount ||
       aXs.Length() != aCount ||
@@ -210,7 +196,6 @@ void
 nsBrowserElement::GoBack(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->GoBack();
 
@@ -223,7 +208,6 @@ void
 nsBrowserElement::GoForward(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->GoForward();
 
@@ -236,7 +220,6 @@ void
 nsBrowserElement::Reload(bool aHardReload, ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->Reload(aHardReload);
 
@@ -249,7 +232,6 @@ void
 nsBrowserElement::Stop(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->Stop();
 
@@ -264,7 +246,6 @@ nsBrowserElement::Download(const nsAString& aUrl,
                            ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsCOMPtr<nsIXPConnectWrappedJS> wrappedObj = do_QueryInterface(mBrowserElementAPI);
@@ -295,7 +276,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::PurgeHistory(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->PurgeHistory(getter_AddRefs(req));
@@ -315,7 +295,6 @@ nsBrowserElement::GetScreenshot(uint32_t aWidth,
                                 ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetScreenshot(aWidth, aHeight, aMimeType,
@@ -337,7 +316,6 @@ void
 nsBrowserElement::Zoom(float aZoom, ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->Zoom(aZoom);
 
@@ -350,7 +328,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::GetCanGoBack(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetCanGoBack(getter_AddRefs(req));
@@ -367,7 +344,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::GetCanGoForward(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetCanGoForward(getter_AddRefs(req));
@@ -384,7 +360,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::GetContentDimensions(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetContentDimensions(getter_AddRefs(req));
@@ -403,7 +378,6 @@ nsBrowserElement::FindAll(const nsAString& aSearchString,
                           ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   uint32_t caseSensitivity;
   if (aCaseSensitivity == BrowserFindCaseSensitivity::Case_insensitive) {
@@ -424,7 +398,6 @@ nsBrowserElement::FindNext(BrowserFindDirection aDirection,
                           ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   uint32_t direction;
   if (aDirection == BrowserFindDirection::Backward) {
@@ -444,7 +417,6 @@ void
 nsBrowserElement::ClearMatch(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->ClearMatch();
 
@@ -633,7 +605,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::GetMuted(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetMuted(getter_AddRefs(req));
@@ -650,7 +621,6 @@ void
 nsBrowserElement::Mute(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->Mute();
 
@@ -663,7 +633,6 @@ void
 nsBrowserElement::Unmute(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->Unmute();
 
@@ -676,7 +645,6 @@ already_AddRefed<DOMRequest>
 nsBrowserElement::GetVolume(ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsresult rv = mBrowserElementAPI->GetVolume(getter_AddRefs(req));
@@ -693,7 +661,6 @@ void
 nsBrowserElement::SetVolume(float aVolume, ErrorResult& aRv)
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
-  NS_ENSURE_TRUE_VOID(IsNotWidgetOrThrow(aRv));
 
   nsresult rv = mBrowserElementAPI->SetVolume(aVolume);
 
@@ -720,7 +687,6 @@ nsBrowserElement::ExecuteScript(const nsAString& aScript,
                                 ErrorResult& aRv)
 {
   NS_ENSURE_TRUE(IsBrowserElementOrThrow(aRv), nullptr);
-  NS_ENSURE_TRUE(IsNotWidgetOrThrow(aRv), nullptr);
 
   nsCOMPtr<nsIDOMDOMRequest> req;
   nsCOMPtr<nsIXPConnectWrappedJS> wrappedObj = do_QueryInterface(mBrowserElementAPI);
diff --git a/dom/html/nsBrowserElement.h b/dom/html/nsBrowserElement.h
index 03c28e47bc95..ea431e5f5633 100644
--- a/dom/html/nsBrowserElement.h
+++ b/dom/html/nsBrowserElement.h
@@ -34,7 +34,7 @@ class ErrorResult;
 class nsBrowserElement
 {
 public:
-  nsBrowserElement() : mOwnerIsWidget(false) {}
+  nsBrowserElement() {}
   virtual ~nsBrowserElement() {}
 
   void SetVisible(bool aVisible, ErrorResult& aRv);
@@ -136,8 +136,6 @@ protected:
 
 private:
   bool IsBrowserElementOrThrow(ErrorResult& aRv);
-  bool IsNotWidgetOrThrow(ErrorResult& aRv);
-  bool mOwnerIsWidget;
 };
 
 } // namespace mozilla
diff --git a/dom/html/nsGenericHTMLFrameElement.cpp b/dom/html/nsGenericHTMLFrameElement.cpp
index 4608ba28fc5f..3132f544142a 100644
--- a/dom/html/nsGenericHTMLFrameElement.cpp
+++ b/dom/html/nsGenericHTMLFrameElement.cpp
@@ -507,10 +507,6 @@ nsGenericHTMLFrameElement::GetReallyIsBrowserOrApp(bool *aOut)
   uint32_t permission = nsIPermissionManager::DENY_ACTION;
   nsresult rv = permMgr->TestPermissionFromPrincipal(principal, "browser", &permission);
   NS_ENSURE_SUCCESS(rv, NS_OK);
-  if (permission != nsIPermissionManager::ALLOW_ACTION) {
-    rv = permMgr->TestPermissionFromPrincipal(principal, "embed-widgets", &permission);
-    NS_ENSURE_SUCCESS(rv, NS_OK);
-  }
   *aOut = permission == nsIPermissionManager::ALLOW_ACTION;
   return NS_OK;
 }
@@ -527,20 +523,6 @@ nsGenericHTMLFrameElement::GetReallyIsApp(bool *aOut)
 
 namespace {
 
-bool WidgetsEnabled()
-{
-  static bool sMozWidgetsEnabled = false;
-  static bool sBoolVarCacheInitialized = false;
-
-  if (!sBoolVarCacheInitialized) {
-    sBoolVarCacheInitialized = true;
-    Preferences::AddBoolVarCache(&sMozWidgetsEnabled,
-                                 "dom.enable_widgets");
-  }
-
-  return sMozWidgetsEnabled;
-}
-
 bool NestedEnabled()
 {
   static bool sMozNestedEnabled = false;
@@ -557,26 +539,6 @@ bool NestedEnabled()
 
 } // namespace
 
-/* [infallible] */ NS_IMETHODIMP
-nsGenericHTMLFrameElement::GetReallyIsWidget(bool *aOut)
-{
-  *aOut = false;
-  if (!WidgetsEnabled()) {
-    return NS_OK;
-  }
-
-  nsAutoString appManifestURL;
-  GetManifestURLByType(nsGkAtoms::mozapp, appManifestURL);
-  bool isApp = !appManifestURL.IsEmpty();
-
-  nsAutoString widgetManifestURL;
-  GetManifestURLByType(nsGkAtoms::mozwidget, widgetManifestURL);
-  bool isWidget = !widgetManifestURL.IsEmpty();
-
-  *aOut = isWidget && !isApp;
-  return NS_OK;
-}
-
 /* [infallible] */ NS_IMETHODIMP
 nsGenericHTMLFrameElement::GetIsolated(bool *aOut)
 {
@@ -591,20 +553,15 @@ nsGenericHTMLFrameElement::GetIsolated(bool *aOut)
   return NS_OK;
 }
 
-/** Get manifest url of app or widget
- * @param AppType: nsGkAtoms::mozapp or nsGkAtoms::mozwidget
+/*
+ * Get manifest url of app.
  */
-void nsGenericHTMLFrameElement::GetManifestURLByType(nsIAtom *aAppType,
-                                                     nsAString& aManifestURL)
+void nsGenericHTMLFrameElement::GetManifestURL(nsAString& aManifestURL)
 {
   aManifestURL.Truncate();
 
-  if (aAppType != nsGkAtoms::mozapp && aAppType != nsGkAtoms::mozwidget) {
-    return;
-  }
-
   nsAutoString manifestURL;
-  GetAttr(kNameSpaceID_None, aAppType, manifestURL);
+  GetAttr(kNameSpaceID_None, nsGkAtoms::mozapp, manifestURL);
   if (manifestURL.IsEmpty()) {
     return;
   }
@@ -613,8 +570,7 @@ void nsGenericHTMLFrameElement::GetManifestURLByType(nsIAtom *aAppType,
   nsCOMPtr<nsIPermissionManager> permMgr = services::GetPermissionManager();
   NS_ENSURE_TRUE_VOID(permMgr);
   nsIPrincipal *principal = NodePrincipal();
-  const char* aPermissionType = (aAppType == nsGkAtoms::mozapp) ? "embed-apps"
-                                                                : "embed-widgets";
+  const char* aPermissionType = "embed-apps";
   uint32_t permission = nsIPermissionManager::DENY_ACTION;
   nsresult rv = permMgr->TestPermissionFromPrincipal(principal,
                                                      aPermissionType,
@@ -634,17 +590,6 @@ void nsGenericHTMLFrameElement::GetManifestURLByType(nsIAtom *aAppType,
     return;
   }
 
-  bool hasWidgetPage = false;
-  nsAutoString src;
-  if (aAppType == nsGkAtoms::mozwidget) {
-    GetAttr(kNameSpaceID_None, nsGkAtoms::src, src);
-    nsresult rv = app->HasWidgetPage(src, &hasWidgetPage);
-
-    if (!NS_SUCCEEDED(rv) || !hasWidgetPage) {
-      return;
-    }
-  }
-
   aManifestURL.Assign(manifestURL);
 }
 
@@ -668,32 +613,24 @@ nsGenericHTMLFrameElement::GetAppManifestURL(nsAString& aOut)
   }
 
   nsAutoString appManifestURL;
-  nsAutoString widgetManifestURL;
 
-  GetManifestURLByType(nsGkAtoms::mozapp, appManifestURL);
-
-  if (WidgetsEnabled()) {
-    GetManifestURLByType(nsGkAtoms::mozwidget, widgetManifestURL);
-  }
+  GetManifestURL(appManifestURL);
 
   bool isApp = !appManifestURL.IsEmpty();
-  bool isWidget = !widgetManifestURL.IsEmpty();
 
-  if (!isApp && !isWidget) {
+  if (!isApp) {
     // No valid case to get manifest
     return NS_OK;
   }
 
-  if (isApp && isWidget) {
-    NS_WARNING("Can not simultaneously be mozapp and mozwidget");
+  if (isApp) {
+    NS_WARNING("Can not simultaneously be mozapp");
     return NS_OK;
   }
 
   nsAutoString manifestURL;
   if (isApp) {
     manifestURL.Assign(appManifestURL);
-  } else if (isWidget) {
-    manifestURL.Assign(widgetManifestURL);
   }
 
   aOut.Assign(manifestURL);
diff --git a/dom/html/nsGenericHTMLFrameElement.h b/dom/html/nsGenericHTMLFrameElement.h
index dac606cea2a6..03b3d78cd0b1 100644
--- a/dom/html/nsGenericHTMLFrameElement.h
+++ b/dom/html/nsGenericHTMLFrameElement.h
@@ -125,7 +125,7 @@ protected:
   bool mFullscreenFlag = false;
 
 private:
-  void GetManifestURLByType(nsIAtom *aAppType, nsAString& aOut);
+  void GetManifestURL(nsAString& aOut);
 };
 
 #endif // nsGenericHTMLFrameElement_h
diff --git a/dom/interfaces/apps/mozIApplication.idl b/dom/interfaces/apps/mozIApplication.idl
index 9a53261f8a68..7aa2b8d29021 100644
--- a/dom/interfaces/apps/mozIApplication.idl
+++ b/dom/interfaces/apps/mozIApplication.idl
@@ -19,12 +19,6 @@ interface mozIApplication: nsISupports
   /* Return true if this app has |permission|. */
   boolean hasPermission(in string permission);
 
-  /**
-   *  Return true if this app can be a widget and
-   *  its |widgetPages| contains |page|
-   */
-  boolean hasWidgetPage(in DOMString pageURL);
-
   /* Application status as defined in nsIPrincipal. */
   readonly attribute unsigned short appStatus;
 
diff --git a/dom/interfaces/html/nsIMozBrowserFrame.idl b/dom/interfaces/html/nsIMozBrowserFrame.idl
index abf495a9e0af..a9dccdd1ceea 100644
--- a/dom/interfaces/html/nsIMozBrowserFrame.idl
+++ b/dom/interfaces/html/nsIMozBrowserFrame.idl
@@ -25,24 +25,11 @@ interface nsIMozBrowserFrame : nsIDOMMozBrowserFrame
    * Gets whether this frame really is an app frame.
    *
    * In order to really be an app frame, this frame must really be a browser
-   * frame (this requirement will go away eventually), and must satisfy one
-   * and only one of the following conditions:
-   * 1. the frame's mozapp attribute must point to the manifest of a valid app
-   * 2. the frame's mozwidget attribute must point to the manifest of a valid
-   * app, and the src should be in the |widgetPages| specified by the manifest.
+   * frame (this requirement will go away eventually), and  the frame's mozapp
+   * attribute must point to the manifest of a valid app.
    */
   [infallible] readonly attribute boolean reallyIsApp;
 
-  /**
-   * Gets whether this frame really is a widget frame.
-   *
-   * In order to really be a frame, this frame must really be a browser
-   * frame (this requirement will go away eventually), the frame's mozwidget
-   * attribute must point to the manifest of a valid app, and the src should
-   * be in the |widgetPages| specified by the manifest.
-   */
-  [infallible] readonly attribute boolean reallyIsWidget;
-
   /**
    * Gets whether this frame is an isolated frame.
    *
@@ -58,8 +45,7 @@ interface nsIMozBrowserFrame : nsIDOMMozBrowserFrame
   [infallible] readonly attribute boolean isolated;
 
   /**
-   * Gets this frame's app manifest URL or widget manifest URL, if the frame
-   * really is an app frame.
+   * Gets this frame's app manifest URL, if the frame really is an app frame.
    * Otherwise, returns the empty string.
    *
    * This method is guaranteed not to fail.
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index d3c5c3473a71..e900b7639103 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -965,7 +965,7 @@ pref("devtools.debugger.prompt-connection", true);
 // Block tools from seeing / interacting with certified apps
 pref("devtools.debugger.forbid-certified-apps", true);
 // List of permissions that a sideloaded app can't ask for
-pref("devtools.apps.forbidden-permissions", "embed-apps,embed-widgets");
+pref("devtools.apps.forbidden-permissions", "embed-apps");
 
 // DevTools default color unit
 pref("devtools.defaultColorUnit", "authored");