diff --git a/accessible/jsat/AccessFu.jsm b/accessible/jsat/AccessFu.jsm
index 4cfbfc2fa3..e0d8ecb493 100644
--- a/accessible/jsat/AccessFu.jsm
+++ b/accessible/jsat/AccessFu.jsm
@@ -340,9 +340,9 @@ this.AccessFu = { // jshint ignore:line
       case 'remote-browser-shown':
       case 'inprocess-browser-shown':
       {
-        // Ignore notifications that aren't from a BrowserOrApp
+        // Ignore notifications that aren't from a Browser
         let frameLoader = aSubject.QueryInterface(Ci.nsIFrameLoader);
-        if (!frameLoader.ownerIsMozBrowserOrAppFrame) {
+        if (!frameLoader.ownerIsMozBrowserFrame) {
           return;
         }
         this._handleMessageManager(frameLoader.messageManager);
diff --git a/caps/nsIPrincipal.idl b/caps/nsIPrincipal.idl
index 03f293f7b2..f197021caa 100644
--- a/caps/nsIPrincipal.idl
+++ b/caps/nsIPrincipal.idl
@@ -303,15 +303,6 @@ interface nsIPrincipal : nsISerializable
      */
     [infallible] readonly attribute unsigned long privateBrowsingId;
 
-    /**
-     * Returns true iff the principal is inside an isolated mozbrowser element.
-     * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
-     * mozbrowser elements.  <iframe mozbrowser noisolation> does not count as
-     * isolated since isolation is disabled.  Isolation can only be disabled if
-     * the containing document is chrome.
-     */
-    [infallible] readonly attribute boolean isInIsolatedMozBrowserElement;
-
     /**
      * Returns true if this principal has an unknown appId. This shouldn't
      * generally be used. We only expose it due to not providing the correct
diff --git a/caps/nsScriptSecurityManager.cpp b/caps/nsScriptSecurityManager.cpp
index 7394bf0f74..9c70115482 100644
--- a/caps/nsScriptSecurityManager.cpp
+++ b/caps/nsScriptSecurityManager.cpp
@@ -243,63 +243,7 @@ nsScriptSecurityManager::SecurityHashURI(nsIURI* aURI)
 uint16_t
 nsScriptSecurityManager::AppStatusForPrincipal(nsIPrincipal *aPrin)
 {
-    uint32_t appId = aPrin->GetAppId();
-
-    // After bug 1238160, the principal no longer knows how to answer "is this a
-    // browser element", which is really what this code path wants. Currently,
-    // desktop is the only platform where we intend to disable isolation on a
-    // browser frame, so non-desktop should be able to assume that
-    // inIsolatedMozBrowser is true for all mozbrowser frames.  Additionally,
-    // apps are no longer used on desktop, so appId is always NO_APP_ID.  We use
-    // a release assertion in nsFrameLoader::OwnerIsIsolatedMozBrowserFrame so
-    // that platforms with apps can assume inIsolatedMozBrowser is true for all
-    // mozbrowser frames.
-    bool inIsolatedMozBrowser = aPrin->GetIsInIsolatedMozBrowserElement();
-
-    NS_WARNING_ASSERTION(
-      appId != nsIScriptSecurityManager::UNKNOWN_APP_ID,
-      "Asking for app status on a principal with an unknown app id");
-
-    // Installed apps have a valid app id (not NO_APP_ID or UNKNOWN_APP_ID)
-    // and they are not inside a mozbrowser.
-    if (appId == nsIScriptSecurityManager::NO_APP_ID ||
-        appId == nsIScriptSecurityManager::UNKNOWN_APP_ID ||
-        inIsolatedMozBrowser)
-    {
-        return nsIPrincipal::APP_STATUS_NOT_INSTALLED;
-    }
-
-    nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-    NS_ENSURE_TRUE(appsService, nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-
-    nsCOMPtr<mozIApplication> app;
-    appsService->GetAppByLocalId(appId, getter_AddRefs(app));
-    NS_ENSURE_TRUE(app, nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-
-    uint16_t status = nsIPrincipal::APP_STATUS_INSTALLED;
-    NS_ENSURE_SUCCESS(app->GetAppStatus(&status),
-                      nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-
-    nsString appOrigin;
-    NS_ENSURE_SUCCESS(app->GetOrigin(appOrigin),
-                      nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-    nsCOMPtr<nsIURI> appURI;
-    NS_ENSURE_SUCCESS(NS_NewURI(getter_AddRefs(appURI), appOrigin),
-                      nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-
-    // The app could contain a cross-origin iframe - make sure that the content
-    // is actually same-origin with the app.
-    MOZ_ASSERT(inIsolatedMozBrowser == false, "Checked this above");
-    nsAutoCString suffix;
-    PrincipalOriginAttributes attrs;
-    NS_ENSURE_TRUE(attrs.PopulateFromOrigin(NS_ConvertUTF16toUTF8(appOrigin), suffix),
-                   nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-    attrs.mAppId = appId;
-    attrs.mInIsolatedMozBrowser = false;
-    nsCOMPtr<nsIPrincipal> appPrin = BasePrincipal::CreateCodebasePrincipal(appURI, attrs);
-    NS_ENSURE_TRUE(appPrin, nsIPrincipal::APP_STATUS_NOT_INSTALLED);
-    return aPrin->Equals(appPrin) ? status
-                                  : nsIPrincipal::APP_STATUS_NOT_INSTALLED;
+    return nsIPrincipal::APP_STATUS_NOT_INSTALLED;
 }
 
 /*
diff --git a/devtools/server/actors/webconsole.js b/devtools/server/actors/webconsole.js
index 106b0e4e04..45414326ef 100644
--- a/devtools/server/actors/webconsole.js
+++ b/devtools/server/actors/webconsole.js
@@ -569,11 +569,9 @@ WebConsoleActor.prototype =
 
     let startedListeners = [];
     let window = !this.parentActor.isRootActor ? this.window : null;
-    let appId = null;
     let messageManager = null;
 
     if (this._parentIsContentActor) {
-      appId = this.parentActor.docShell.appId;
       messageManager = this.parentActor.messageManager;
     }
 
@@ -604,16 +602,16 @@ WebConsoleActor.prototype =
             // Create a StackTraceCollector that's going to be shared both by the
             // NetworkMonitorChild (getting messages about requests from parent) and
             // by the NetworkMonitor that directly watches service workers requests.
-            this.stackTraceCollector = new StackTraceCollector({ window, appId });
+            this.stackTraceCollector = new StackTraceCollector({ window });
             this.stackTraceCollector.init();
 
             let processBoundary = Services.appinfo.processType !=
                                   Ci.nsIXULRuntime.PROCESS_TYPE_DEFAULT;
-            if ((appId || messageManager) && processBoundary) {
+            if (messageManager && processBoundary) {
               // Start a network monitor in the parent process to listen to
               // most requests than happen in parent
               this.networkMonitor =
-                new NetworkMonitorChild(appId, this.parentActor.outerWindowID,
+                new NetworkMonitorChild(this.parentActor.outerWindowID,
                                         messageManager, this.conn, this);
               this.networkMonitor.init();
               // Spawn also one in the child to listen to service workers
diff --git a/devtools/shared/layout/utils.js b/devtools/shared/layout/utils.js
index bbe6df4c85..c6b996bebf 100644
--- a/devtools/shared/layout/utils.js
+++ b/devtools/shared/layout/utils.js
@@ -37,12 +37,12 @@ function getTopWindow(win) {
                     .getInterface(Ci.nsIWebNavigation)
                     .QueryInterface(Ci.nsIDocShell);
 
-  if (!docShell.isMozBrowserOrApp) {
+  if (!docShell.isMozBrowser) {
     return win.top;
   }
 
   let topDocShell =
-    docShell.getSameTypeRootTreeItemIgnoreBrowserAndAppBoundaries();
+    docShell.getSameTypeRootTreeItemIgnoreBrowserBoundaries();
 
   return topDocShell
           ? topDocShell.contentViewer.DOMDocument.defaultView
@@ -98,12 +98,12 @@ function getParentWindow(win) {
                  .getInterface(Ci.nsIWebNavigation)
                  .QueryInterface(Ci.nsIDocShell);
 
-  if (!docShell.isMozBrowserOrApp) {
+  if (!docShell.isMozBrowser) {
     return win.parent;
   }
 
   let parentDocShell =
-    docShell.getSameTypeParentIgnoreBrowserAndAppBoundaries();
+    docShell.getSameTypeParentIgnoreBrowserBoundaries();
 
   return parentDocShell
           ? parentDocShell.contentViewer.DOMDocument.defaultView
diff --git a/devtools/shared/webconsole/network-monitor.js b/devtools/shared/webconsole/network-monitor.js
index 4488fc1df7..0725ebc2a1 100644
--- a/devtools/shared/webconsole/network-monitor.js
+++ b/devtools/shared/webconsole/network-monitor.js
@@ -1551,8 +1551,6 @@ NetworkMonitor.prototype = {
  * data to the WebConsoleActor or to a NetworkEventActor.
  *
  * @constructor
- * @param number appId
- *        The web appId of the child process.
  * @param number outerWindowID
  *        The outerWindowID of the TabActor's main window.
  * @param nsIMessageManager messageManager
@@ -1562,8 +1560,7 @@ NetworkMonitor.prototype = {
  * @param object owner
  *        The WebConsoleActor that is listening for the network requests.
  */
-function NetworkMonitorChild(appId, outerWindowID, messageManager, conn, owner) {
-  this.appId = appId;
+function NetworkMonitorChild(outerWindowID, messageManager, conn, owner) {
   this.outerWindowID = outerWindowID;
   this.conn = conn;
   this.owner = owner;
@@ -1577,7 +1574,6 @@ function NetworkMonitorChild(appId, outerWindowID, messageManager, conn, owner)
 exports.NetworkMonitorChild = NetworkMonitorChild;
 
 NetworkMonitorChild.prototype = {
-  appId: null,
   owner: null,
   _netEvents: null,
   _saveRequestAndResponseBodies: true,
@@ -1623,7 +1619,6 @@ NetworkMonitorChild.prototype = {
     mm.addMessageListener(`${this._msgName}:newEvent`, this._onNewEvent);
     mm.addMessageListener(`${this._msgName}:updateEvent`, this._onUpdateEvent);
     mm.sendAsyncMessage(this._msgName, {
-      appId: this.appId,
       outerWindowID: this.outerWindowID,
       action: "start",
     });
diff --git a/docshell/base/LoadContext.cpp b/docshell/base/LoadContext.cpp
index 4c265e4246..db750ead9c 100644
--- a/docshell/base/LoadContext.cpp
+++ b/docshell/base/LoadContext.cpp
@@ -157,28 +157,6 @@ LoadContext::SetRemoteTabs(bool aUseRemoteTabs)
   return NS_ERROR_UNEXPECTED;
 }
 
-NS_IMETHODIMP
-LoadContext::GetIsInIsolatedMozBrowserElement(bool* aIsInIsolatedMozBrowserElement)
-{
-  MOZ_ASSERT(mIsNotNull);
-
-  NS_ENSURE_ARG_POINTER(aIsInIsolatedMozBrowserElement);
-
-  *aIsInIsolatedMozBrowserElement = mOriginAttributes.mInIsolatedMozBrowser;
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-LoadContext::GetAppId(uint32_t* aAppId)
-{
-  MOZ_ASSERT(mIsNotNull);
-
-  NS_ENSURE_ARG_POINTER(aAppId);
-
-  *aAppId = mOriginAttributes.mAppId;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 LoadContext::GetOriginAttributes(JS::MutableHandleValue aAttrs)
 {
diff --git a/docshell/base/LoadContext.h b/docshell/base/LoadContext.h
index 90a6a600b8..9714128d8d 100644
--- a/docshell/base/LoadContext.h
+++ b/docshell/base/LoadContext.h
@@ -38,8 +38,6 @@ public:
   NS_DECL_NSILOADCONTEXT
   NS_DECL_NSIINTERFACEREQUESTOR
 
-  // appId/inIsolatedMozBrowser arguments override those in SerializedLoadContext
-  // provided by child process.
   LoadContext(const IPC::SerializedLoadContext& aToCopy,
               dom::Element* aTopFrameElement,
               DocShellOriginAttributes& aAttrs)
@@ -54,8 +52,6 @@ public:
   {
   }
 
-  // appId/inIsolatedMozBrowser arguments override those in SerializedLoadContext
-  // provided by child process.
   LoadContext(const IPC::SerializedLoadContext& aToCopy,
               uint64_t aNestedFrameId,
               DocShellOriginAttributes& aAttrs)
diff --git a/docshell/base/nsDSURIContentListener.cpp b/docshell/base/nsDSURIContentListener.cpp
index cac2a1786c..30213a9833 100644
--- a/docshell/base/nsDSURIContentListener.cpp
+++ b/docshell/base/nsDSURIContentListener.cpp
@@ -334,7 +334,7 @@ nsDSURIContentListener::CheckOneFrameOptionsPolicy(nsIHttpChannel* aHttpChannel,
            curDocShellItem->GetParent(getter_AddRefs(parentDocShellItem))) &&
          parentDocShellItem) {
     nsCOMPtr<nsIDocShell> curDocShell = do_QueryInterface(curDocShellItem);
-    if (curDocShell && curDocShell->GetIsMozBrowserOrApp()) {
+    if (curDocShell && curDocShell->GetIsMozBrowser()) {
       break;
     }
 
diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index 7ad4be98da..39cee20f1f 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -2569,7 +2569,7 @@ nsDocShell::GetFullscreenAllowed(bool* aFullscreenAllowed)
 NS_IMETHODIMP
 nsDocShell::SetFullscreenAllowed(bool aFullscreenAllowed)
 {
-  if (!nsIDocShell::GetIsMozBrowserOrApp()) {
+  if (!nsIDocShell::GetIsMozBrowser()) {
     // Only allow setting of fullscreenAllowed on content/process boundaries.
     // At non-boundaries the fullscreenAllowed attribute is calculated based on
     // whether all enclosing frames have the "mozFullscreenAllowed" attribute
@@ -3401,7 +3401,7 @@ nsDocShell::GetSameTypeParent(nsIDocShellTreeItem** aParent)
   NS_ENSURE_ARG_POINTER(aParent);
   *aParent = nullptr;
 
-  if (nsIDocShell::GetIsMozBrowserOrApp()) {
+  if (nsIDocShell::GetIsMozBrowser()) {
     return NS_OK;
   }
 
@@ -3418,7 +3418,7 @@ nsDocShell::GetSameTypeParent(nsIDocShellTreeItem** aParent)
 }
 
 NS_IMETHODIMP
-nsDocShell::GetSameTypeParentIgnoreBrowserAndAppBoundaries(nsIDocShell** aParent)
+nsDocShell::GetSameTypeParentIgnoreBrowserBoundaries(nsIDocShell** aParent)
 {
   NS_ENSURE_ARG_POINTER(aParent);
   *aParent = nullptr;
@@ -3472,18 +3472,18 @@ nsDocShell::GetSameTypeRootTreeItem(nsIDocShellTreeItem** aRootTreeItem)
 }
 
 NS_IMETHODIMP
-nsDocShell::GetSameTypeRootTreeItemIgnoreBrowserAndAppBoundaries(nsIDocShell ** aRootTreeItem)
+nsDocShell::GetSameTypeRootTreeItemIgnoreBrowserBoundaries(nsIDocShell ** aRootTreeItem)
 {
     NS_ENSURE_ARG_POINTER(aRootTreeItem);
     *aRootTreeItem = static_cast<nsIDocShell *>(this);
 
     nsCOMPtr<nsIDocShell> parent;
-    NS_ENSURE_SUCCESS(GetSameTypeParentIgnoreBrowserAndAppBoundaries(getter_AddRefs(parent)),
+    NS_ENSURE_SUCCESS(GetSameTypeParentIgnoreBrowserBoundaries(getter_AddRefs(parent)),
                       NS_ERROR_FAILURE);
     while (parent) {
       *aRootTreeItem = parent;
       NS_ENSURE_SUCCESS((*aRootTreeItem)->
-        GetSameTypeParentIgnoreBrowserAndAppBoundaries(getter_AddRefs(parent)),
+        GetSameTypeParentIgnoreBrowserBoundaries(getter_AddRefs(parent)),
         NS_ERROR_FAILURE);
     }
     NS_ADDREF(*aRootTreeItem);
@@ -3537,12 +3537,6 @@ nsDocShell::CanAccessItem(nsIDocShellTreeItem* aTargetItem,
     return false;
   }
 
-  if (targetDS->GetIsInIsolatedMozBrowserElement() !=
-        accessingDS->GetIsInIsolatedMozBrowserElement() ||
-      targetDS->GetAppId() != accessingDS->GetAppId()) {
-    return false;
-  }
-
   nsCOMPtr<nsIDocShellTreeItem> accessingRoot;
   aAccessingItem->GetSameTypeRootTreeItem(getter_AddRefs(accessingRoot));
   nsCOMPtr<nsIDocShell> accessingRootDS = do_QueryInterface(accessingRoot);
@@ -3563,7 +3557,7 @@ nsDocShell::CanAccessItem(nsIDocShellTreeItem* aTargetItem,
   if (OriginAttributes::IsFirstPartyEnabled()) {
     if (accessingDS == accessingRootDS &&
         aAccessingItem->ItemType() == nsIDocShellTreeItem::typeContent &&
-        !accessingDS->GetIsMozBrowserOrApp()) {
+        !accessingDS->GetIsMozBrowser()) {
 
       nsCOMPtr<nsIDocument> accessingDoc = aAccessingItem->GetDocument();
 
@@ -3577,7 +3571,7 @@ nsDocShell::CanAccessItem(nsIDocShellTreeItem* aTargetItem,
 
     if (targetDS == targetRootDS &&
         aTargetItem->ItemType() == nsIDocShellTreeItem::typeContent &&
-        !targetDS->GetIsMozBrowserOrApp()) {
+        !targetDS->GetIsMozBrowser()) {
 
       nsCOMPtr<nsIDocument> targetDoc = aAccessingItem->GetDocument();
 
@@ -3774,7 +3768,7 @@ nsDocShell::DoFindItemWithName(const nsAString& aName,
 
     // If we have a same-type parent, respecting browser and app boundaries.
     // NOTE: Could use GetSameTypeParent if the issues described in bug 1310344 are fixed.
-    if (!GetIsMozBrowserOrApp() && parentAsTreeItem->ItemType() == mItemType) {
+    if (!GetIsMozBrowser() && parentAsTreeItem->ItemType() == mItemType) {
       return parentAsTreeItem->FindItemWithName(
         aName,
         static_cast<nsIDocShellTreeItem*>(this),
@@ -5312,16 +5306,6 @@ nsDocShell::LoadErrorPage(nsIURI* aURI, const char16_t* aURL,
   errorPageUrl.AppendLiteral("&f=");
   errorPageUrl.AppendASCII(frameType.get());
 
-  // Append the manifest URL if the error comes from an app.
-  nsString manifestURL;
-  nsresult rv = GetAppManifestURL(manifestURL);
-  if (manifestURL.Length() > 0) {
-    nsCString manifestParam;
-    SAFE_ESCAPE(manifestParam, NS_ConvertUTF16toUTF8(manifestURL), url_Path);
-    errorPageUrl.AppendLiteral("&m=");
-    errorPageUrl.AppendASCII(manifestParam.get());
-  }
-
   nsCOMPtr<nsICaptivePortalService> cps = do_GetService(NS_CAPTIVEPORTAL_CID);
   int32_t cpsState;
   if (cps && NS_SUCCEEDED(cps->GetState(&cpsState)) &&
@@ -5335,7 +5319,7 @@ nsDocShell::LoadErrorPage(nsIURI* aURI, const char16_t* aURL,
   errorPageUrl.AppendASCII(escapedDescription.get());
 
   nsCOMPtr<nsIURI> errorPageURI;
-  rv = NS_NewURI(getter_AddRefs(errorPageURI), errorPageUrl);
+  nsresult rv = NS_NewURI(getter_AddRefs(errorPageURI), errorPageUrl);
   NS_ENSURE_SUCCESS(rv, rv);
 
   return InternalLoad(errorPageURI, nullptr, false, false,
@@ -6222,9 +6206,7 @@ nsDocShell::SetIsActive(bool aIsActive)
     mScriptGlobal->SetIsBackground(!aIsActive);
     if (nsCOMPtr<nsIDocument> doc = mScriptGlobal->GetExtantDoc()) {
       // Update orientation when the top-level browsing context becomes active.
-      // We make an exception for apps because they currently rely on
-      // orientation locks persisting across browsing contexts.
-      if (aIsActive && !GetIsApp()) {
+      if (aIsActive) {
         nsCOMPtr<nsIDocShellTreeItem> parent;
         GetSameTypeParent(getter_AddRefs(parent));
         if (!parent) {
@@ -6261,7 +6243,7 @@ nsDocShell::SetIsActive(bool aIsActive)
       continue;
     }
 
-    if (!docshell->GetIsMozBrowserOrApp()) {
+    if (!docshell->GetIsMozBrowser()) {
       docshell->SetIsActive(aIsActive);
     }
   }
@@ -10636,9 +10618,7 @@ nsDocShell::InternalLoad(nsIURI* aURI,
   // lock the orientation of the document to the document's default
   // orientation. We don't explicitly check for a top-level browsing context
   // here because orientation is only set on top-level browsing contexts.
-  // We make an exception for apps because they currently rely on
-  // orientation locks persisting across browsing contexts.
-  if (OrientationLock() != eScreenOrientation_None && !GetIsApp()) {
+  if (OrientationLock() != eScreenOrientation_None) {
 #ifdef DEBUG
     nsCOMPtr<nsIDocShellTreeItem> parent;
     GetSameTypeParent(getter_AddRefs(parent));
@@ -11023,7 +11003,7 @@ nsDocShell::DoURILoad(nsIURI* aURI,
   NeckoOriginAttributes neckoAttrs;
   bool isTopLevelDoc = aContentPolicyType == nsIContentPolicy::TYPE_DOCUMENT &&
                        mItemType == typeContent &&
-                       !GetIsMozBrowserOrApp();
+                       !GetIsMozBrowser();
   neckoAttrs.InheritFromDocShellToNecko(GetOriginAttributes(), isTopLevelDoc, aURI);
   rv = loadInfo->SetOriginAttributes(neckoAttrs);
   if (NS_WARN_IF(NS_FAILED(rv))) {
@@ -14480,16 +14460,9 @@ nsDocShell::GetFrameType(uint32_t* aFrameType)
 }
 
 /* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetIsApp(bool* aIsApp)
+nsDocShell::GetIsMozBrowser(bool* aIsMozBrowser)
 {
-  *aIsApp = (mFrameType == FRAME_TYPE_APP);
-  return NS_OK;
-}
-
-/* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetIsMozBrowserOrApp(bool* aIsMozBrowserOrApp)
-{
-  *aIsMozBrowserOrApp = (mFrameType != FRAME_TYPE_REGULAR);
+  *aIsMozBrowser = (mFrameType == FRAME_TYPE_BROWSER);
   return NS_OK;
 }
 
@@ -14512,30 +14485,9 @@ nsDocShell::GetInheritedFrameType()
 }
 
 /* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetIsIsolatedMozBrowserElement(bool* aIsIsolatedMozBrowserElement)
+nsDocShell::GetIsInMozBrowser(bool* aIsInMozBrowser)
 {
-  bool result = mFrameType == FRAME_TYPE_BROWSER &&
-                mOriginAttributes.mInIsolatedMozBrowser;
-  *aIsIsolatedMozBrowserElement = result;
-  return NS_OK;
-}
-
-/* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetIsInIsolatedMozBrowserElement(bool* aIsInIsolatedMozBrowserElement)
-{
-  MOZ_ASSERT(!mOriginAttributes.mInIsolatedMozBrowser ||
-             (GetInheritedFrameType() == FRAME_TYPE_BROWSER),
-             "Isolated mozbrowser should only be true inside browser frames");
-  bool result = (GetInheritedFrameType() == FRAME_TYPE_BROWSER) &&
-                mOriginAttributes.mInIsolatedMozBrowser;
-  *aIsInIsolatedMozBrowserElement = result;
-  return NS_OK;
-}
-
-/* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetIsInMozBrowserOrApp(bool* aIsInMozBrowserOrApp)
-{
-  *aIsInMozBrowserOrApp = (GetInheritedFrameType() != FRAME_TYPE_REGULAR);
+  *aIsInMozBrowser = (GetInheritedFrameType() == FRAME_TYPE_BROWSER);
   return NS_OK;
 }
 
@@ -14553,25 +14505,6 @@ nsDocShell::GetIsTopLevelContentDocShell(bool* aIsTopLevelContentDocShell)
   return NS_OK;
 }
 
-/* [infallible] */ NS_IMETHODIMP
-nsDocShell::GetAppId(uint32_t* aAppId)
-{
-  if (mOriginAttributes.mAppId != nsIScriptSecurityManager::UNKNOWN_APP_ID) {
-    *aAppId = mOriginAttributes.mAppId;
-    return NS_OK;
-  }
-
-  nsCOMPtr<nsIDocShell> parent;
-  GetSameTypeParentIgnoreBrowserAndAppBoundaries(getter_AddRefs(parent));
-
-  if (!parent) {
-    *aAppId = nsIScriptSecurityManager::NO_APP_ID;
-    return NS_OK;
-  }
-
-  return parent->GetAppId(aAppId);
-}
-
 // Implements nsILoadContext.originAttributes
 NS_IMETHODIMP
 nsDocShell::GetOriginAttributes(JS::MutableHandle<JS::Value> aVal)
@@ -14680,23 +14613,6 @@ nsDocShell::SetOriginAttributes(JS::Handle<JS::Value> aOriginAttributes,
   return SetOriginAttributes(attrs);
 }
 
-NS_IMETHODIMP
-nsDocShell::GetAppManifestURL(nsAString& aAppManifestURL)
-{
-  uint32_t appId = nsIDocShell::GetAppId();
-  if (appId != nsIScriptSecurityManager::NO_APP_ID &&
-      appId != nsIScriptSecurityManager::UNKNOWN_APP_ID) {
-    nsCOMPtr<nsIAppsService> appsService =
-      do_GetService(APPS_SERVICE_CONTRACTID);
-    NS_ASSERTION(appsService, "No AppsService available");
-    appsService->GetManifestURLByLocalId(appId, aAppManifestURL);
-  } else {
-    aAppManifestURL.SetLength(0);
-  }
-
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsDocShell::GetAsyncPanZoomEnabled(bool* aOut)
 {
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index 396996ea74..2bb71911b9 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -789,8 +789,6 @@ protected:
   static const nsCString FrameTypeToString(uint32_t aFrameType)
   {
     switch (aFrameType) {
-      case FRAME_TYPE_APP:
-        return NS_LITERAL_CSTRING("app");
       case FRAME_TYPE_BROWSER:
         return NS_LITERAL_CSTRING("browser");
       case FRAME_TYPE_REGULAR:
diff --git a/docshell/base/nsIDocShell.idl b/docshell/base/nsIDocShell.idl
index d2812bd9c9..516d3981c4 100644
--- a/docshell/base/nsIDocShell.idl
+++ b/docshell/base/nsIDocShell.idl
@@ -826,109 +826,50 @@ interface nsIDocShell : nsIDocShellTreeItem
    */
   [noscript] void notifyScrollObservers();
 
-  /**
-   * Returns true iff the docshell corresponds to an <iframe mozapp>.
-   */
-  [infallible] readonly attribute boolean isApp;
-
   /**
    * The type of iframe that this docshell lives.
    */
   const unsigned long FRAME_TYPE_REGULAR = 0;
   const unsigned long FRAME_TYPE_BROWSER = 1;
-  const unsigned long FRAME_TYPE_APP     = 2;
 
   [infallible] attribute unsigned long frameType;
 
   /**
-   * Returns true if this docshell corresponds to an <iframe mozbrowser> or
-   * <iframe mozapp>.  <xul:browser> returns false here.
+   * Returns true if this docshell corresponds to an <iframe mozbrowser>.
+   * <xul:browser> returns false here.
    */
-  [infallible] readonly attribute boolean isMozBrowserOrApp;
+  [infallible] readonly attribute boolean isMozBrowser;
 
   /**
-   * Returns true if this docshell corresponds to an isolated <iframe
-   * mozbrowser>.
-   *
-   * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
-   * mozbrowser elements.  <iframe mozbrowser noisolation> does not count as
-   * isolated since isolation is disabled.  Isolation can only be disabled if
-   * the containing document is chrome.
-   */
-  [infallible] readonly attribute boolean isIsolatedMozBrowserElement;
-
-  /**
-   * Returns true if this docshell corresponds to an isolated <iframe
-   * mozbrowser> or if the docshell is contained in an isolated <iframe
-   * mozbrowser>.
-   *
-   * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
-   * mozbrowser elements.  <iframe mozbrowser noisolation> does not count as
-   * isolated since isolation is disabled.  Isolation can only be disabled if
-   * the containing document is chrome.
-   *
-   * Our notion here of "contained in" means: Walk up the docshell hierarchy in
-   * this process until we hit an <iframe mozapp> or <iframe mozbrowser> (or
-   * until the hierarchy ends).  Return true iff the docshell we stopped on has
-   * isIsolatedMozBrowserElement == true.
-   */
-  [infallible] readonly attribute boolean isInIsolatedMozBrowserElement;
-
-  /**
-   * Returns true if this docshell corresponds to an <iframe mozbrowser> or
-   * <iframe mozapp>, or if this docshell is contained in an <iframe mozbrowser>
-   * or <iframe mozapp>.  <xul:browser> returns false here.
+   * Returns true if this docshell corresponds to an <iframe mozbrowser>, or
+   * if this docshell is contained in an <iframe mozbrowser>. <xul:browser>
+   * returns false here.
    *
    * To compute this value, we walk up the docshell hierarchy.  If we encounter
-   * a docshell with isMozBrowserOrApp before we hit the end of the hierarchy,
+   * a docshell with isMozBrowser before we hit the end of the hierarchy,
    * we return true.  Otherwise, we return false.
    */
-  [infallible] readonly attribute boolean isInMozBrowserOrApp;
+  [infallible] readonly attribute boolean isInMozBrowser;
 
   /**
    * Returns true if this docshell is the top level content docshell.
    */
   [infallible] readonly attribute boolean isTopLevelContentDocShell;
 
-  /**
-   * Returns the id of the app associated with this docshell.  If this docshell
-   * is an <iframe mozbrowser> inside an <iframe mozapp>, we return the app's
-   * appId.
-   *
-   * We compute this value by walking up the docshell hierarchy until we find a
-   * docshell on which origin attributes was set. (ignoring those docshells
-   * where x == UNKNOWN_APP_ID).  We return the app id x.
-   *
-   * If we don't find a docshell with an associated app id in our hierarchy, we
-   * return NO_APP_ID.  We never return UNKNOWN_APP_ID.
-   *
-   * Notice that a docshell may have an associated app even if it returns true
-   * for isBrowserElement!
-   */
-  [infallible] readonly attribute unsigned long appId;
-
-  /**
-   * Return the manifest URL of the app associated with this docshell.
-   *
-   * If there is no associated app in our hierarchy, we return empty string.
-   */
-  readonly attribute DOMString appManifestURL;
-
   /**
    * Like nsIDocShellTreeItem::GetSameTypeParent, except this ignores <iframe
-   * mozbrowser> and <iframe mozapp> boundaries.
+   * mozbrowser> boundaries.
    */
-  nsIDocShell getSameTypeParentIgnoreBrowserAndAppBoundaries();
+  nsIDocShell getSameTypeParentIgnoreBrowserBoundaries();
 
   /**
    * Like nsIDocShellTreeItem::GetSameTypeRootTreeItem, except this ignores
-   * <iframe mozbrowser> and <iframe mozapp> boundaries.
+   * <iframe mozbrowser> boundaries.
    */
-  nsIDocShell getSameTypeRootTreeItemIgnoreBrowserAndAppBoundaries();
+  nsIDocShell getSameTypeRootTreeItemIgnoreBrowserBoundaries();
 
   /**
-   * True iff asynchronous panning and zooming is enabled for this
-   * docshell.
+   * True if asynchronous panning and zooming is enabled for this docshell.
    */
   readonly attribute bool asyncPanZoomEnabled;
 
diff --git a/docshell/base/nsIDocShellTreeItem.idl b/docshell/base/nsIDocShellTreeItem.idl
index 431b16c797..e2a3168f32 100644
--- a/docshell/base/nsIDocShellTreeItem.idl
+++ b/docshell/base/nsIDocShellTreeItem.idl
@@ -57,10 +57,9 @@ interface nsIDocShellTreeItem : nsISupports
 
 	/*
 	This getter returns the same thing parent does however if the parent
-	is of a different itemType, or if the parent is an <iframe mozbrowser>
-	or <iframe mozapp>, it will instead return nullptr.  This call is a
-	convience function for those wishing to not cross the boundaries at
-	which item types change.
+	is of a different itemType, or if the parent is an <iframe mozbrowser>.
+	It will instead return nullptr.  This call is a convience function for
+	Ithose wishing to not cross the boundaries at which item types change.
 	*/
 	readonly attribute nsIDocShellTreeItem sameTypeParent;
 
diff --git a/docshell/base/nsILoadContext.idl b/docshell/base/nsILoadContext.idl
index b318c1a5e8..3894a12e34 100644
--- a/docshell/base/nsILoadContext.idl
+++ b/docshell/base/nsILoadContext.idl
@@ -104,21 +104,6 @@ interface nsILoadContext : nsISupports
    */
   [noscript] void SetRemoteTabs(in boolean aUseRemoteTabs);
 
-  /**
-   * Returns true iff the load is occurring inside an isolated mozbrowser
-   * element. <iframe mozbrowser mozapp> and <xul:browser> are not considered to
-   * be mozbrowser elements.  <iframe mozbrowser noisolation> does not count as
-   * isolated since isolation is disabled.  Isolation can only be disabled if
-   * the containing document is chrome.
-   */
-  readonly attribute boolean isInIsolatedMozBrowserElement;
-
-  /**
-   * Returns the app id of the app the load is occurring is in. Returns
-   * nsIScriptSecurityManager::NO_APP_ID if the load is not part of an app.
-   */
-  readonly attribute unsigned long appId;
-
   /**
    * A dictionary of the non-default origin attributes associated with this
    * nsILoadContext.
diff --git a/dom/apps/PermissionsTable.jsm b/dom/apps/PermissionsTable.jsm
index 7c6a8490fc..550d73d6c7 100644
--- a/dom/apps/PermissionsTable.jsm
+++ b/dom/apps/PermissionsTable.jsm
@@ -233,11 +233,6 @@ this.PermissionsTable =  { geolocation: {
                              privileged: DENY_ACTION,
                              certified: ALLOW_ACTION
                            },
-                           "embed-apps": {
-                             app: DENY_ACTION,
-                             privileged: DENY_ACTION,
-                             certified: ALLOW_ACTION
-                           },
                            "background-sensors": {
                              app: DENY_ACTION,
                              privileged: DENY_ACTION,
diff --git a/dom/base/Navigator.cpp b/dom/base/Navigator.cpp
index 026ae15836..9ff4519d82 100644
--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -63,7 +63,6 @@
 #include "TimeManager.h"
 #include "nsStreamUtils.h"
 #include "nsIAppsService.h"
-#include "mozIApplication.h"
 #include "WidgetUtils.h"
 #include "mozilla/dom/MediaDevices.h"
 #include "MediaManager.h"
diff --git a/dom/base/ThirdPartyUtil.cpp b/dom/base/ThirdPartyUtil.cpp
index 8c0ba80bf8..39f72eb546 100644
--- a/dom/base/ThirdPartyUtil.cpp
+++ b/dom/base/ThirdPartyUtil.cpp
@@ -17,6 +17,7 @@
 #include "nsIURI.h"
 #include "nsThreadUtils.h"
 #include "mozilla/Logging.h"
+#include "nsPIDOMWindow.h"
 
 NS_IMPL_ISUPPORTS(ThirdPartyUtil, mozIThirdPartyUtil)
 
@@ -145,7 +146,7 @@ ThirdPartyUtil::IsThirdPartyWindow(mozIDOMWindowProxy* aWindow,
   nsCOMPtr<nsIURI> parentURI;
   do {
     // We use GetScriptableParent rather than GetParent because we consider
-    // <iframe mozbrowser/mozapp> to be a top-level frame.
+    // <iframe mozbrowser> to be a top-level frame.
     parent = current->GetScriptableParent();
     if (SameCOMIdentity(parent, current)) {
       // We're at the topmost content window. We already know the answer.
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 5d5edbd3b3..155d55ac29 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -6616,7 +6616,7 @@ nsContentUtils::IsUserFocusIgnored(nsINode* aNode)
     nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(aNode);
     if (browserFrame &&
         aNode->AsElement()->HasAttr(kNameSpaceID_None, nsGkAtoms::ignoreuserfocus) &&
-        browserFrame->GetReallyIsBrowserOrApp()) {
+        browserFrame->GetReallyIsBrowser()) {
       return true;
     }
     nsPIDOMWindowOuter* win = aNode->OwnerDoc()->GetWindow();
diff --git a/dom/base/nsFrameLoader.cpp b/dom/base/nsFrameLoader.cpp
index 645a392594..9c10b9af08 100644
--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -12,7 +12,6 @@
 
 #include "prenv.h"
 
-#include "mozIApplication.h"
 #include "nsDocShell.h"
 #include "nsIAppsService.h"
 #include "nsIDOMHTMLIFrameElement.h"
@@ -88,7 +87,6 @@
 #include "mozilla/dom/Element.h"
 #include "mozilla/jsipc/CrossProcessObjectWrappers.h"
 #include "mozilla/layout/RenderFrameParent.h"
-#include "nsIAppsService.h"
 #include "GeckoProfiler.h"
 
 #include "jsapi.h"
@@ -1071,12 +1069,6 @@ nsFrameLoader::SwapWithOtherRemoteLoader(nsFrameLoader* aOther,
     return NS_ERROR_NOT_IMPLEMENTED;
   }
 
-  if (mRemoteBrowser->IsIsolatedMozBrowserElement() !=
-      aOther->mRemoteBrowser->IsIsolatedMozBrowserElement() ||
-      mRemoteBrowser->HasOwnApp() != aOther->mRemoteBrowser->HasOwnApp()) {
-    return NS_ERROR_NOT_IMPLEMENTED;
-  }
-
   // When we swap docShells, maybe we have to deal with a new page created just
   // for this operation. In this case, the browser code should already have set
   // the correct userContextId attribute value in the owning XULElement, but our
@@ -1145,10 +1137,10 @@ nsFrameLoader::SwapWithOtherRemoteLoader(nsFrameLoader* aOther,
   }
 
   // Destroy browser frame scripts for content leaving a frame with browser API
-  if (OwnerIsMozBrowserOrAppFrame() && !aOther->OwnerIsMozBrowserOrAppFrame()) {
+  if (OwnerIsMozBrowserFrame() && !aOther->OwnerIsMozBrowserFrame()) {
     DestroyBrowserFrameScripts();
   }
-  if (!OwnerIsMozBrowserOrAppFrame() && aOther->OwnerIsMozBrowserOrAppFrame()) {
+  if (!OwnerIsMozBrowserFrame() && aOther->OwnerIsMozBrowserFrame()) {
     aOther->DestroyBrowserFrameScripts();
   }
 
@@ -1320,12 +1312,12 @@ nsFrameLoader::SwapWithOtherLoader(nsFrameLoader* aOther,
 
   bool ourFullscreenAllowed =
     ourContent->IsXULElement() ||
-    (OwnerIsMozBrowserOrAppFrame() &&
+    (OwnerIsMozBrowserFrame() &&
       (ourContent->HasAttr(kNameSpaceID_None, nsGkAtoms::allowfullscreen) ||
        ourContent->HasAttr(kNameSpaceID_None, nsGkAtoms::mozallowfullscreen)));
   bool otherFullscreenAllowed =
     otherContent->IsXULElement() ||
-    (aOther->OwnerIsMozBrowserOrAppFrame() &&
+    (aOther->OwnerIsMozBrowserFrame() &&
       (otherContent->HasAttr(kNameSpaceID_None, nsGkAtoms::allowfullscreen) ||
        otherContent->HasAttr(kNameSpaceID_None, nsGkAtoms::mozallowfullscreen)));
   if (ourFullscreenAllowed != otherFullscreenAllowed) {
@@ -1470,12 +1462,6 @@ nsFrameLoader::SwapWithOtherLoader(nsFrameLoader* aOther,
     return NS_ERROR_NOT_IMPLEMENTED;
   }
 
-  if (ourDocshell->GetIsIsolatedMozBrowserElement() !=
-      otherDocshell->GetIsIsolatedMozBrowserElement() ||
-      ourDocshell->GetIsApp() != otherDocshell->GetIsApp()) {
-    return NS_ERROR_NOT_IMPLEMENTED;
-  }
-
   // When we swap docShells, maybe we have to deal with a new page created just
   // for this operation. In this case, the browser code should already have set
   // the correct userContextId attribute value in the owning XULElement, but our
@@ -1522,10 +1508,10 @@ nsFrameLoader::SwapWithOtherLoader(nsFrameLoader* aOther,
   }
 
   // Destroy browser frame scripts for content leaving a frame with browser API
-  if (OwnerIsMozBrowserOrAppFrame() && !aOther->OwnerIsMozBrowserOrAppFrame()) {
+  if (OwnerIsMozBrowserFrame() && !aOther->OwnerIsMozBrowserFrame()) {
     DestroyBrowserFrameScripts();
   }
-  if (!OwnerIsMozBrowserOrAppFrame() && aOther->OwnerIsMozBrowserOrAppFrame()) {
+  if (!OwnerIsMozBrowserFrame() && aOther->OwnerIsMozBrowserFrame()) {
     aOther->DestroyBrowserFrameScripts();
   }
 
@@ -1884,102 +1870,20 @@ nsFrameLoader::SetOwnerContent(Element* aContent)
 }
 
 bool
-nsFrameLoader::OwnerIsMozBrowserOrAppFrame()
+nsFrameLoader::OwnerIsMozBrowserFrame()
 {
   nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
-  return browserFrame ? browserFrame->GetReallyIsBrowserOrApp() : false;
+  return browserFrame ? browserFrame->GetReallyIsBrowser() : false;
 }
 
 // The xpcom getter version
 NS_IMETHODIMP
-nsFrameLoader::GetOwnerIsMozBrowserOrAppFrame(bool* aResult)
+nsFrameLoader::GetOwnerIsMozBrowserFrame(bool* aResult)
 {
-  *aResult = OwnerIsMozBrowserOrAppFrame();
+  *aResult = OwnerIsMozBrowserFrame();
   return NS_OK;
 }
 
-bool
-nsFrameLoader::OwnerIsAppFrame()
-{
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
-  return browserFrame ? browserFrame->GetReallyIsApp() : false;
-}
-
-bool
-nsFrameLoader::OwnerIsMozBrowserFrame()
-{
-  return OwnerIsMozBrowserOrAppFrame() && !OwnerIsAppFrame();
-}
-
-bool
-nsFrameLoader::OwnerIsIsolatedMozBrowserFrame()
-{
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
-  if (!browserFrame) {
-    return false;
-  }
-
-  if (!OwnerIsMozBrowserFrame()) {
-    return false;
-  }
-
-  bool isolated = browserFrame->GetIsolated();
-  if (isolated) {
-    return true;
-  }
-
-  return false;
-}
-
-void
-nsFrameLoader::GetOwnerAppManifestURL(nsAString& aOut)
-{
-  aOut.Truncate();
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
-  if (browserFrame) {
-    browserFrame->GetAppManifestURL(aOut);
-  }
-}
-
-already_AddRefed<mozIApplication>
-nsFrameLoader::GetOwnApp()
-{
-  nsAutoString manifest;
-  GetOwnerAppManifestURL(manifest);
-  if (manifest.IsEmpty()) {
-    return nullptr;
-  }
-
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  NS_ENSURE_TRUE(appsService, nullptr);
-
-  nsCOMPtr<mozIApplication> app;
-  appsService->GetAppByManifestURL(manifest, getter_AddRefs(app));
-
-  return app.forget();
-}
-
-already_AddRefed<mozIApplication>
-nsFrameLoader::GetContainingApp()
-{
-  // See if our owner content's principal has an associated app.
-  uint32_t appId = mOwnerContent->NodePrincipal()->GetAppId();
-  MOZ_ASSERT(appId != nsIScriptSecurityManager::UNKNOWN_APP_ID);
-
-  if (appId == nsIScriptSecurityManager::NO_APP_ID ||
-      appId == nsIScriptSecurityManager::UNKNOWN_APP_ID) {
-    return nullptr;
-  }
-
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  NS_ENSURE_TRUE(appsService, nullptr);
-
-  nsCOMPtr<mozIApplication> app;
-  appsService->GetAppByLocalId(appId, getter_AddRefs(app));
-
-  return app.forget();
-}
-
 bool
 nsFrameLoader::ShouldUseRemoteProcess()
 {
@@ -2003,7 +1907,7 @@ nsFrameLoader::ShouldUseRemoteProcess()
 
   // If we're an <iframe mozbrowser> and we don't have a "remote" attribute,
   // fall back to the default.
-  if (OwnerIsMozBrowserOrAppFrame() &&
+  if (OwnerIsMozBrowserFrame() &&
       !mOwnerContent->HasAttr(kNameSpaceID_None, nsGkAtoms::Remote)) {
 
     return Preferences::GetBool("dom.ipc.browser_frames.oop_by_default", false);
@@ -2011,7 +1915,7 @@ nsFrameLoader::ShouldUseRemoteProcess()
 
   // Otherwise, we're remote if we have "remote=true" and we're either a
   // browser frame or a XUL element.
-  return (OwnerIsMozBrowserOrAppFrame() ||
+  return (OwnerIsMozBrowserFrame() ||
           mOwnerContent->GetNameSpaceID() == kNameSpaceID_XUL) &&
          mOwnerContent->AttrValueIs(kNameSpaceID_None,
                                     nsGkAtoms::Remote,
@@ -2189,13 +2093,13 @@ nsFrameLoader::MaybeCreateDocShell()
   // Inherit origin attributes from parent document if
   // 1. It's in a content docshell.
   // 2. its nodePrincipal is not a SystemPrincipal.
-  // 3. It's not a mozbrowser nor mozapp frame.
+  // 3. It's not a mozbrowser frame.
   //
   // For example, firstPartyDomain is computed from top-level document, it
   // doesn't exist in the top-level docshell.
   if (parentType == nsIDocShellTreeItem::typeContent &&
       !nsContentUtils::IsSystemPrincipal(doc->NodePrincipal()) &&
-      !OwnerIsMozBrowserOrAppFrame()) {
+      !OwnerIsMozBrowserFrame()) {
     PrincipalOriginAttributes poa = BasePrincipal::Cast(doc->NodePrincipal())->OriginAttributesRef();
 
     // Assert on the firstPartyDomain from top-level docshell should be empty
@@ -2210,42 +2114,14 @@ nsFrameLoader::MaybeCreateDocShell()
               "docshell and document should have the same appId attribute.");
     MOZ_ASSERT(attrs.mUserContextId == poa.mUserContextId,
               "docshell and document should have the same userContextId attribute.");
-    MOZ_ASSERT(attrs.mInIsolatedMozBrowser == poa.mInIsolatedMozBrowser,
-              "docshell and document should have the same inIsolatedMozBrowser attribute.");
     MOZ_ASSERT(attrs.mPrivateBrowsingId == poa.mPrivateBrowsingId,
               "docshell and document should have the same privateBrowsingId attribute.");
 
     attrs.InheritFromDocToChildDocShell(poa);
   }
 
-  if (OwnerIsAppFrame()) {
-    // You can't be both an app and a browser frame.
-    MOZ_ASSERT(!OwnerIsMozBrowserFrame());
-
-    nsCOMPtr<mozIApplication> ownApp = GetOwnApp();
-    MOZ_ASSERT(ownApp);
-    uint32_t ownAppId = nsIScriptSecurityManager::NO_APP_ID;
-    if (ownApp) {
-      NS_ENSURE_SUCCESS(ownApp->GetLocalId(&ownAppId), NS_ERROR_FAILURE);
-    }
-
-    attrs.mAppId = ownAppId;
-    mDocShell->SetFrameType(nsIDocShell::FRAME_TYPE_APP);
-  }
-
   if (OwnerIsMozBrowserFrame()) {
-    // You can't be both a browser and an app frame.
-    MOZ_ASSERT(!OwnerIsAppFrame());
-
-    nsCOMPtr<mozIApplication> containingApp = GetContainingApp();
-    uint32_t containingAppId = nsIScriptSecurityManager::NO_APP_ID;
-    if (containingApp) {
-      NS_ENSURE_SUCCESS(containingApp->GetLocalId(&containingAppId),
-                        NS_ERROR_FAILURE);
-    }
-
-    attrs.mAppId = containingAppId;
-    attrs.mInIsolatedMozBrowser = OwnerIsIsolatedMozBrowserFrame();
+    attrs.mAppId = nsIScriptSecurityManager::NO_APP_ID;
     mDocShell->SetFrameType(nsIDocShell::FRAME_TYPE_BROWSER);
   }
 
@@ -2276,7 +2152,7 @@ nsFrameLoader::MaybeCreateDocShell()
   }
   attrs.SyncAttributesWithPrivateBrowsing(isPrivate);
 
-  if (OwnerIsMozBrowserOrAppFrame()) {
+  if (OwnerIsMozBrowserFrame()) {
     // For inproc frames, set the docshell properties.
     nsAutoString name;
     if (mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::name, name)) {
@@ -2675,7 +2551,7 @@ nsFrameLoader::TryRemoteBrowser()
   }
 
   // <iframe mozbrowser> gets to skip these checks.
-  if (!OwnerIsMozBrowserOrAppFrame()) {
+  if (!OwnerIsMozBrowserFrame()) {
     if (parentDocShell->ItemType() != nsIDocShellTreeItem::typeChrome) {
       return false;
     }
@@ -2716,8 +2592,8 @@ nsFrameLoader::TryRemoteBrowser()
   NS_ENSURE_SUCCESS(rv, false);
 
   nsCOMPtr<Element> ownerElement = mOwnerContent;
-  mRemoteBrowser = ContentParent::CreateBrowserOrApp(context, ownerElement,
-                                                     openerContentParent, mFreshProcess);
+  mRemoteBrowser = ContentParent::CreateBrowser(context, ownerElement,
+                                                openerContentParent, mFreshProcess);
   if (!mRemoteBrowser) {
     return false;
   }
@@ -2980,7 +2856,7 @@ nsFrameLoader::EnsureMessageManager()
   }
 
   if (!mIsTopLevelContent &&
-      !OwnerIsMozBrowserOrAppFrame() &&
+      !OwnerIsMozBrowserFrame() &&
       !IsRemoteFrame() &&
       !(mOwnerContent->IsXULElement() &&
         mOwnerContent->AttrValueIs(kNameSpaceID_None,
@@ -3287,7 +3163,7 @@ nsFrameLoader::GetLoadContext(nsILoadContext** aLoadContext)
 void
 nsFrameLoader::InitializeBrowserAPI()
 {
-  if (!OwnerIsMozBrowserOrAppFrame()) {
+  if (!OwnerIsMozBrowserFrame()) {
     return;
   }
   if (!IsRemoteFrame()) {
@@ -3311,7 +3187,7 @@ nsFrameLoader::InitializeBrowserAPI()
 void
 nsFrameLoader::DestroyBrowserFrameScripts()
 {
-  if (!OwnerIsMozBrowserOrAppFrame()) {
+  if (!OwnerIsMozBrowserFrame()) {
     return;
   }
   nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
@@ -3392,24 +3268,10 @@ nsresult
 nsFrameLoader::GetNewTabContext(MutableTabContext* aTabContext,
                                 nsIURI* aURI)
 {
-  nsCOMPtr<mozIApplication> ownApp = GetOwnApp();
-  nsCOMPtr<mozIApplication> containingApp = GetContainingApp();
   DocShellOriginAttributes attrs;
-  attrs.mInIsolatedMozBrowser = OwnerIsIsolatedMozBrowserFrame();
   nsresult rv;
 
-  // Get the AppId from ownApp
-  uint32_t appId = nsIScriptSecurityManager::NO_APP_ID;
-  if (ownApp) {
-    rv = ownApp->GetLocalId(&appId);
-    NS_ENSURE_SUCCESS(rv, rv);
-    NS_ENSURE_STATE(appId != nsIScriptSecurityManager::NO_APP_ID);
-  } else if (containingApp) {
-    rv = containingApp->GetLocalId(&appId);
-    NS_ENSURE_SUCCESS(rv, rv);
-    NS_ENSURE_STATE(appId != nsIScriptSecurityManager::NO_APP_ID);
-  }
-  attrs.mAppId = appId;
+  attrs.mAppId = nsIScriptSecurityManager::NO_APP_ID; // No longer used...
 
   // set the userContextId on the attrs before we pass them into
   // the tab context
@@ -3439,8 +3301,6 @@ nsFrameLoader::GetNewTabContext(MutableTabContext* aTabContext,
   bool tabContextUpdated =
     aTabContext->SetTabContext(OwnerIsMozBrowserFrame(),
                                mIsPrerendered,
-                               ownApp,
-                               containingApp,
                                showAccelerators,
                                showFocusRings,
                                attrs);
diff --git a/dom/base/nsFrameLoader.h b/dom/base/nsFrameLoader.h
index 39fb5c1888..900997572e 100644
--- a/dom/base/nsFrameLoader.h
+++ b/dom/base/nsFrameLoader.h
@@ -241,53 +241,18 @@ private:
    */
   bool IsRemoteFrame();
 
-  /**
-   * Is this a frameloader for a bona fide <iframe mozbrowser> or
-   * <iframe mozapp>?  (I.e., does the frame return true for
-   * nsIMozBrowserFrame::GetReallyIsBrowserOrApp()?)
-   * <xul:browser> is not a mozbrowser or app, so this is false for that case.
-   */
-  bool OwnerIsMozBrowserOrAppFrame();
-
-  /**
-   * Is this a frameloader for a bona fide <iframe mozapp>?  (I.e., does the
-   * frame return true for nsIMozBrowserFrame::GetReallyIsApp()?)
-   */
-  bool OwnerIsAppFrame();
-
   /**
    * Is this a frame loader for a bona fide <iframe mozbrowser>?
    * <xul:browser> is not a mozbrowser, so this is false for that case.
    */
   bool OwnerIsMozBrowserFrame();
 
-  /**
-   * Is this a frame loader for an isolated <iframe mozbrowser>?
-   *
-   * By default, mozbrowser frames are isolated.  Isolation can be disabled by
-   * setting the frame's noisolation attribute.  Disabling isolation is
-   * only allowed if the containing document is chrome.
-   */
-  bool OwnerIsIsolatedMozBrowserFrame();
-
   /**
    * Get our owning element's app manifest URL, or return the empty string if
    * our owning element doesn't have an app manifest URL.
    */
   void GetOwnerAppManifestURL(nsAString& aOut);
 
-  /**
-   * Get the app for our frame.  This is the app whose manifest is returned by
-   * GetOwnerAppManifestURL.
-   */
-  already_AddRefed<mozIApplication> GetOwnApp();
-
-  /**
-   * Get the app which contains this frame.  This is the app associated with
-   * the frame element's principal.
-   */
-  already_AddRefed<mozIApplication> GetContainingApp();
-
   /**
    * If we are an IPC frame, set mRemoteFrame. Otherwise, create and
    * initialize mDocShell.
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index de1a4927be..617aea60a7 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -101,7 +101,6 @@ GK_ATOM(animations, "animations")
 GK_ATOM(anonid, "anonid")
 GK_ATOM(anonlocation, "anonlocation")
 GK_ATOM(any, "any")
-GK_ATOM(mozapp, "mozapp")
 GK_ATOM(applet, "applet")
 GK_ATOM(applyImports, "apply-imports")
 GK_ATOM(applyTemplates, "apply-templates")
@@ -665,7 +664,6 @@ GK_ATOM(nodeSet, "node-set")
 GK_ATOM(noembed, "noembed")
 GK_ATOM(noframes, "noframes")
 GK_ATOM(nohref, "nohref")
-GK_ATOM(noisolation, "noisolation")
 GK_ATOM(nomodule, "nomodule")
 GK_ATOM(nonce, "nonce")
 GK_ATOM(none, "none")
@@ -1003,7 +1001,6 @@ GK_ATOM(panel, "panel")
 GK_ATOM(param, "param")
 GK_ATOM(parameter, "parameter")
 GK_ATOM(parent, "parent")
-GK_ATOM(parentapp, "parentapp")
 GK_ATOM(parentfocused, "parentfocused")
 GK_ATOM(parsetype, "parsetype")
 GK_ATOM(password, "password")
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 5ec720dfef..42d38b9e10 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -4485,7 +4485,7 @@ nsGlobalWindow::GetParentOuter()
   }
 
   nsCOMPtr<nsPIDOMWindowOuter> parent;
-  if (mDocShell->GetIsMozBrowserOrApp()) {
+  if (mDocShell->GetIsMozBrowser()) {
     parent = AsOuter();
   } else {
     parent = GetParent();
@@ -4543,7 +4543,7 @@ nsGlobalWindow::GetParent()
   }
 
   nsCOMPtr<nsIDocShell> parent;
-  mDocShell->GetSameTypeParentIgnoreBrowserAndAppBoundaries(getter_AddRefs(parent));
+  mDocShell->GetSameTypeParentIgnoreBrowserBoundaries(getter_AddRefs(parent));
 
   if (parent) {
     nsCOMPtr<nsPIDOMWindowOuter> win = parent->GetWindow();
@@ -4662,9 +4662,9 @@ nsGlobalWindow::GetContentInternal(ErrorResult& aError, bool aUnprivilegedCaller
     return domWindow.forget();
   }
 
-  // If we're contained in <iframe mozbrowser> or <iframe mozapp>, then
-  // GetContent is the same as window.top.
-  if (mDocShell && mDocShell->GetIsInMozBrowserOrApp()) {
+  // If we're contained in <iframe mozbrowser>, then GetContent is the same as
+  // window.top.
+  if (mDocShell && mDocShell->GetIsInMozBrowser()) {
     return GetTopOuter();
   }
 
@@ -7992,7 +7992,7 @@ nsGlobalWindow::ResizeToOuter(int32_t aWidth, int32_t aHeight, ErrorResult& aErr
    * If caller is a browser-element then dispatch a resize event to
    * the embedder.
    */
-  if (mDocShell && mDocShell->GetIsMozBrowserOrApp()) {
+  if (mDocShell && mDocShell->GetIsMozBrowser()) {
     CSSIntSize size(aWidth, aHeight);
     if (!DispatchResizeEvent(size)) {
       // The embedder chose to prevent the default action for this
@@ -8042,7 +8042,7 @@ nsGlobalWindow::ResizeByOuter(int32_t aWidthDif, int32_t aHeightDif,
    * If caller is a browser-element then dispatch a resize event to
    * parent.
    */
-  if (mDocShell && mDocShell->GetIsMozBrowserOrApp()) {
+  if (mDocShell && mDocShell->GetIsMozBrowser()) {
     CSSIntSize size;
     if (NS_FAILED(GetInnerSize(size))) {
       return;
@@ -9013,7 +9013,7 @@ nsGlobalWindow::CloseOuter(bool aTrustedCaller)
   MOZ_RELEASE_ASSERT(IsOuterWindow());
 
   if (!mDocShell || IsInModalState() ||
-      (IsFrame() && !mDocShell->GetIsMozBrowserOrApp())) {
+      (IsFrame() && !mDocShell->GetIsMozBrowser())) {
     // window.close() is called on a frame in a frameset, on a window
     // that's already closed, or on a window for which there's
     // currently a modal dialog open. Ignore such calls.
@@ -9034,14 +9034,13 @@ nsGlobalWindow::CloseOuter(bool aTrustedCaller)
     return;
   }
 
-  // Don't allow scripts from content to close non-app or non-neterror
-  // windows that were not opened by script.
+  // Don't allow scripts from content to close non-neterror windows that
+  // were not opened by script.
   nsAutoString url;
   nsresult rv = mDoc->GetURL(url);
   NS_ENSURE_SUCCESS_VOID(rv);
 
-  if (!mDocShell->GetIsApp() &&
-      !StringBeginsWith(url, NS_LITERAL_STRING("about:neterror")) &&
+  if (!StringBeginsWith(url, NS_LITERAL_STRING("about:neterror")) &&
       !mHadOriginalOpener && !aTrustedCaller) {
     bool allowClose = mAllowScriptsToClose ||
       Preferences::GetBool("dom.allow_scripts_to_close_windows", true);
@@ -9489,7 +9488,7 @@ nsGlobalWindow::GetFrameElementOuter(nsIPrincipal& aSubjectPrincipal)
 {
   MOZ_RELEASE_ASSERT(IsOuterWindow());
 
-  if (!mDocShell || mDocShell->GetIsMozBrowserOrApp()) {
+  if (!mDocShell || mDocShell->GetIsMozBrowser()) {
     return nullptr;
   }
 
@@ -9524,7 +9523,7 @@ nsGlobalWindow::GetRealFrameElementOuter()
   }
 
   nsCOMPtr<nsIDocShell> parent;
-  mDocShell->GetSameTypeParentIgnoreBrowserAndAppBoundaries(getter_AddRefs(parent));
+  mDocShell->GetSameTypeParentIgnoreBrowserBoundaries(getter_AddRefs(parent));
 
   if (!parent || parent == mDocShell) {
     // We're at a chrome boundary, don't expose the chrome iframe
diff --git a/dom/base/nsIFrameLoader.idl b/dom/base/nsIFrameLoader.idl
index d840cdce63..d09dd93421 100644
--- a/dom/base/nsIFrameLoader.idl
+++ b/dom/base/nsIFrameLoader.idl
@@ -5,7 +5,6 @@
 
 #include "nsISupports.idl"
 
-interface mozIApplication;
 interface nsFrameLoader;
 interface nsIDocShell;
 interface nsIURI;
@@ -216,11 +215,10 @@ interface nsIFrameLoader : nsISupports
   [infallible] attribute boolean visible;
 
   /**
-   * Find out whether the owner content really is a mozbrowser or app frame
-   * Especially, a widget frame is regarded as an app frame.  <xul:browser> is
-   * not considered to be a mozbrowser frame.
+   * Find out whether the owner content really is a mozbrowser. <xul:browser>
+   * is not considered to be a mozbrowser frame.
    */
-  readonly attribute boolean ownerIsMozBrowserOrAppFrame;
+  readonly attribute boolean ownerIsMozBrowserFrame;
 
   /**
    * The last known width of the frame. Reading this property will not trigger
@@ -265,12 +263,6 @@ interface nsIFrameLoaderOwner : nsISupports
   [binaryname(FrameLoaderXPCOM)] readonly attribute nsIFrameLoader frameLoader;
   [noscript, notxpcom] alreadyAddRefed_nsFrameLoader GetFrameLoader();
 
-  /**
-   * The principal of parent mozIApplication in case of nested mozbrowser
-   * iframes.
-   */
-  readonly attribute mozIApplication parentApplication;
-
   /**
    * Puts the FrameLoaderOwner in prerendering mode.
    */
diff --git a/dom/base/nsInProcessTabChildGlobal.cpp b/dom/base/nsInProcessTabChildGlobal.cpp
index 8e2b56feca..6adfbdaef0 100644
--- a/dom/base/nsInProcessTabChildGlobal.cpp
+++ b/dom/base/nsInProcessTabChildGlobal.cpp
@@ -88,21 +88,24 @@ nsInProcessTabChildGlobal::DoSendAsyncMessage(JSContext* aCx,
 nsInProcessTabChildGlobal::nsInProcessTabChildGlobal(nsIDocShell* aShell,
                                                      nsIContent* aOwner,
                                                      nsFrameMessageManager* aChrome)
-: mDocShell(aShell), mInitialized(false), mLoadingScript(false),
-  mPreventEventsEscaping(false),
-  mOwner(aOwner), mChromeMessageManager(aChrome)
+: mDocShell(aShell)
+, mInitialized(false)
+, mLoadingScript(false)
+, mPreventEventsEscaping(false)
+, mOwner(aOwner)
+, mChromeMessageManager(aChrome)
 {
   SetIsNotDOMBinding();
   mozilla::HoldJSObjects(this);
 
-  // If owner corresponds to an <iframe mozbrowser> or <iframe mozapp>, we'll
+  // If owner corresponds to an <iframe mozbrowser>, we'll have to tweak our
   // GetEventTargetParent implementation.
   nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwner);
   if (browserFrame) {
-    mIsBrowserOrAppFrame = browserFrame->GetReallyIsBrowserOrApp();
+    mIsBrowserFrame = browserFrame->GetReallyIsBrowser();
   }
   else {
-    mIsBrowserOrAppFrame = false;
+    mIsBrowserFrame = false;
   }
 }
 
@@ -272,7 +275,7 @@ nsInProcessTabChildGlobal::GetEventTargetParent(EventChainPreVisitor& aVisitor)
     return NS_OK;
   }
 
-  if (mIsBrowserOrAppFrame &&
+  if (mIsBrowserFrame &&
       (!mOwner || !nsContentUtils::IsInChromeDocshell(mOwner->OwnerDoc()))) {
     if (mOwner) {
       if (nsPIDOMWindowInner* innerWindow = mOwner->OwnerDoc()->GetInnerWindow()) {
diff --git a/dom/base/nsInProcessTabChildGlobal.h b/dom/base/nsInProcessTabChildGlobal.h
index 25193d9c8f..3e52472d6a 100644
--- a/dom/base/nsInProcessTabChildGlobal.h
+++ b/dom/base/nsInProcessTabChildGlobal.h
@@ -165,10 +165,9 @@ protected:
   bool mInitialized;
   bool mLoadingScript;
 
-  // Is this the message manager for an in-process <iframe mozbrowser> or
-  // <iframe mozapp>?  This affects where events get sent, so it affects
-  // GetEventTargetParent.
-  bool mIsBrowserOrAppFrame;
+  // Is this the message manager for an in-process <iframe mozbrowser>? This
+  // affects where events get sent, so it affects GetEventTargetParent.
+  bool mIsBrowserFrame;
   bool mPreventEventsEscaping;
 
   // We keep a strong reference to the frameloader after we've started
diff --git a/dom/base/nsObjectLoadingContent.cpp b/dom/base/nsObjectLoadingContent.cpp
index e508a22f3e..0f0c9106eb 100644
--- a/dom/base/nsObjectLoadingContent.cpp
+++ b/dom/base/nsObjectLoadingContent.cpp
@@ -1250,17 +1250,6 @@ nsObjectLoadingContent::GetFrameLoader()
   return loader.forget();
 }
 
-NS_IMETHODIMP
-nsObjectLoadingContent::GetParentApplication(mozIApplication** aApplication)
-{
-  if (!aApplication) {
-    return NS_ERROR_FAILURE;
-  }
-
-  *aApplication = nullptr;
-  return NS_OK;
-}
-
 void
 nsObjectLoadingContent::PresetOpenerWindow(mozIDOMWindowProxy* aWindow, mozilla::ErrorResult& aRv)
 {
diff --git a/dom/browser-element/BrowserElementChild.js b/dom/browser-element/BrowserElementChild.js
index 066be66d20..a0921a660c 100644
--- a/dom/browser-element/BrowserElementChild.js
+++ b/dom/browser-element/BrowserElementChild.js
@@ -26,7 +26,7 @@ function parentDocShell(docshell) {
 function isTopBrowserElement(docShell) {
   while (docShell) {
     docShell = parentDocShell(docShell);
-    if (docShell && docShell.isMozBrowserOrApp) {
+    if (docShell && docShell.isMozBrowser) {
       return false;
     }
   }
diff --git a/dom/browser-element/BrowserElementCopyPaste.js b/dom/browser-element/BrowserElementCopyPaste.js
index ffb114f840..029538f81c 100644
--- a/dom/browser-element/BrowserElementCopyPaste.js
+++ b/dom/browser-element/BrowserElementCopyPaste.js
@@ -112,7 +112,7 @@ var CopyPasteAssistent = {
       let targetDocShell = currentWindow
           .QueryInterface(Ci.nsIInterfaceRequestor)
           .getInterface(Ci.nsIWebNavigation);
-      if(targetDocShell.isMozBrowserOrApp) {
+      if(targetDocShell.isMozBrowser) {
         break;
       }
     }
diff --git a/dom/browser-element/BrowserElementParent.cpp b/dom/browser-element/BrowserElementParent.cpp
index 46ceb0a3e9..2575d8b506 100644
--- a/dom/browser-element/BrowserElementParent.cpp
+++ b/dom/browser-element/BrowserElementParent.cpp
@@ -54,23 +54,6 @@ CreateIframe(Element* aOpenerFrameElement, const nsAString& aName, bool aRemote)
 
   popupFrameElement->SetMozbrowser(true);
 
-  // Copy the opener frame's mozapp attribute to the popup frame.
-  if (aOpenerFrameElement->HasAttr(kNameSpaceID_None, nsGkAtoms::mozapp)) {
-    nsAutoString mozapp;
-    aOpenerFrameElement->GetAttr(kNameSpaceID_None, nsGkAtoms::mozapp, mozapp);
-    popupFrameElement->SetAttr(kNameSpaceID_None, nsGkAtoms::mozapp,
-                               mozapp, /* aNotify = */ false);
-  }
-
-  // Copy the opener frame's parentApp attribute to the popup frame.
-  if (aOpenerFrameElement->HasAttr(kNameSpaceID_None, nsGkAtoms::parentapp)) {
-    nsAutoString parentApp;
-    aOpenerFrameElement->GetAttr(kNameSpaceID_None, nsGkAtoms::parentapp,
-                                 parentApp);
-    popupFrameElement->SetAttr(kNameSpaceID_None, nsGkAtoms::parentapp,
-                               parentApp, /* aNotify = */ false);
-  }
-
   // Copy the window name onto the iframe.
   popupFrameElement->SetAttr(kNameSpaceID_None, nsGkAtoms::name,
                              aName, /* aNotify = */ false);
diff --git a/dom/events/EventStateManager.cpp b/dom/events/EventStateManager.cpp
index c6089d5d1c..6213367a68 100644
--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -1279,9 +1279,9 @@ EventStateManager::IsRemoteTarget(nsIContent* target) {
     return true;
   }
 
-  // <frame/iframe mozbrowser/mozapp>
+  // <frame/iframe mozbrowser>
   nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(target);
-  if (browserFrame && browserFrame->GetReallyIsBrowserOrApp()) {
+  if (browserFrame && browserFrame->GetReallyIsBrowser()) {
     return !!TabParent::GetFrom(target);
   }
 
diff --git a/dom/html/nsBrowserElement.cpp b/dom/html/nsBrowserElement.cpp
index 5b9100fa1d..1292d7673f 100644
--- a/dom/html/nsBrowserElement.cpp
+++ b/dom/html/nsBrowserElement.cpp
@@ -15,7 +15,6 @@
 
 #include "AudioChannelService.h"
 
-#include "mozIApplication.h"
 #include "nsComponentManagerUtils.h"
 #include "nsContentUtils.h"
 #include "nsFrameLoader.h"
@@ -44,13 +43,13 @@ nsBrowserElement::IsBrowserElementOrThrow(ErrorResult& aRv)
 void
 nsBrowserElement::InitBrowserElementAPI()
 {
-  bool isMozBrowserOrApp;
+  bool isMozBrowser;
   nsCOMPtr<nsIFrameLoader> frameLoader = GetFrameLoader();
   NS_ENSURE_TRUE_VOID(frameLoader);
-  nsresult rv = frameLoader->GetOwnerIsMozBrowserOrAppFrame(&isMozBrowserOrApp);
+  nsresult rv = frameLoader->GetOwnerIsMozBrowserFrame(&isMozBrowser);
   NS_ENSURE_SUCCESS_VOID(rv);
 
-  if (!isMozBrowserOrApp) {
+  if (!isMozBrowser) {
     return;
   }
 
@@ -495,13 +494,13 @@ nsBrowserElement::GetAllowedAudioChannels(
       return;
     }
 
-    bool isMozBrowserOrApp;
-    aRv = frameLoader->GetOwnerIsMozBrowserOrAppFrame(&isMozBrowserOrApp);
+    bool isMozBrowser;
+    aRv = frameLoader->GetOwnerIsMozBrowserFrame(&isMozBrowser);
     if (NS_WARN_IF(aRv.Failed())) {
       return;
     }
 
-    if (!isMozBrowserOrApp) {
+    if (!isMozBrowser) {
       return;
     }
 
diff --git a/dom/html/nsBrowserElement.h b/dom/html/nsBrowserElement.h
index 9a4c47d28a..f98ce97819 100644
--- a/dom/html/nsBrowserElement.h
+++ b/dom/html/nsBrowserElement.h
@@ -123,7 +123,6 @@ public:
 
 protected:
   NS_IMETHOD_(already_AddRefed<nsFrameLoader>) GetFrameLoader() = 0;
-  NS_IMETHOD GetParentApplication(mozIApplication** aApplication) = 0;
 
   void InitBrowserElementAPI();
   void DestroyBrowserElementFrameScripts();
diff --git a/dom/html/nsGenericHTMLFrameElement.cpp b/dom/html/nsGenericHTMLFrameElement.cpp
index 1d0b6769a6..cc51342b7e 100644
--- a/dom/html/nsGenericHTMLFrameElement.cpp
+++ b/dom/html/nsGenericHTMLFrameElement.cpp
@@ -11,10 +11,8 @@
 #include "mozilla/Preferences.h"
 #include "mozilla/ErrorResult.h"
 #include "GeckoProfiler.h"
-#include "mozIApplication.h"
 #include "nsAttrValueInlines.h"
 #include "nsContentUtils.h"
-#include "nsIAppsService.h"
 #include "nsIDocShell.h"
 #include "nsIDOMDocument.h"
 #include "nsIFrame.h"
@@ -191,31 +189,6 @@ nsGenericHTMLFrameElement::GetFrameLoader()
   return loader.forget();
 }
 
-NS_IMETHODIMP
-nsGenericHTMLFrameElement::GetParentApplication(mozIApplication** aApplication)
-{
-  if (!aApplication) {
-    return NS_ERROR_FAILURE;
-  }
-
-  *aApplication = nullptr;
-
-  nsIPrincipal *principal = NodePrincipal();
-  uint32_t appId = principal->GetAppId();
-
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  if (NS_WARN_IF(!appsService)) {
-    return NS_ERROR_FAILURE;
-  }
-
-  nsresult rv = appsService->GetAppByLocalId(appId, aApplication);
-  if (NS_WARN_IF(NS_FAILED(rv))) {
-    return rv;
-  }
-
-  return NS_OK;
-}
-
 void
 nsGenericHTMLFrameElement::PresetOpenerWindow(mozIDOMWindowProxy* aWindow, ErrorResult& aRv)
 {
@@ -512,144 +485,17 @@ nsGenericHTMLFrameElement::BrowserFramesEnabled()
 }
 
 /**
- * Return true if this frame element really is a mozbrowser or mozapp.  (It
+ * Return true if this frame element really is a mozbrowser.  (It
  * needs to have the right attributes, and its creator must have the right
  * permissions.)
  */
 /* [infallible] */ nsresult
-nsGenericHTMLFrameElement::GetReallyIsBrowserOrApp(bool *aOut)
+nsGenericHTMLFrameElement::GetReallyIsBrowser(bool *aOut)
 {
   *aOut = mReallyIsBrowser;
   return NS_OK;
 }
 
-/* [infallible] */ NS_IMETHODIMP
-nsGenericHTMLFrameElement::GetReallyIsApp(bool *aOut)
-{
-  nsAutoString manifestURL;
-  GetAppManifestURL(manifestURL);
-
-  *aOut = !manifestURL.IsEmpty();
-  return NS_OK;
-}
-
-namespace {
-
-bool NestedEnabled()
-{
-  static bool sMozNestedEnabled = false;
-  static bool sBoolVarCacheInitialized = false;
-
-  if (!sBoolVarCacheInitialized) {
-    sBoolVarCacheInitialized = true;
-    Preferences::AddBoolVarCache(&sMozNestedEnabled,
-                                 "dom.ipc.tabs.nested.enabled");
-  }
-
-  return sMozNestedEnabled;
-}
-
-} // namespace
-
-/* [infallible] */ NS_IMETHODIMP
-nsGenericHTMLFrameElement::GetIsolated(bool *aOut)
-{
-  *aOut = true;
-
-  if (!nsContentUtils::IsSystemPrincipal(NodePrincipal())) {
-    return NS_OK;
-  }
-
-  // Isolation is only disabled if the attribute is present
-  *aOut = !HasAttr(kNameSpaceID_None, nsGkAtoms::noisolation);
-  return NS_OK;
-}
-
-/*
- * Get manifest url of app.
- */
-void nsGenericHTMLFrameElement::GetManifestURL(nsAString& aManifestURL)
-{
-  aManifestURL.Truncate();
-
-  nsAutoString manifestURL;
-  GetAttr(kNameSpaceID_None, nsGkAtoms::mozapp, manifestURL);
-  if (manifestURL.IsEmpty()) {
-    return;
-  }
-
-  // Check permission.
-  nsCOMPtr<nsIPermissionManager> permMgr = services::GetPermissionManager();
-  NS_ENSURE_TRUE_VOID(permMgr);
-  nsIPrincipal *principal = NodePrincipal();
-  const char* aPermissionType = "embed-apps";
-  uint32_t permission = nsIPermissionManager::DENY_ACTION;
-  nsresult rv = permMgr->TestPermissionFromPrincipal(principal,
-                                                     aPermissionType,
-                                                     &permission);
-  NS_ENSURE_SUCCESS_VOID(rv);
-  if (permission != nsIPermissionManager::ALLOW_ACTION) {
-    return;
-  }
-
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  NS_ENSURE_TRUE_VOID(appsService);
-
-  nsCOMPtr<mozIApplication> app;
-  appsService->GetAppByManifestURL(manifestURL, getter_AddRefs(app));
-
-  if (!app) {
-    return;
-  }
-
-  aManifestURL.Assign(manifestURL);
-}
-
-NS_IMETHODIMP
-nsGenericHTMLFrameElement::GetAppManifestURL(nsAString& aOut)
-{
-  aOut.Truncate();
-
-  // At the moment, you can't be an app without being a browser.
-  if (!nsIMozBrowserFrame::GetReallyIsBrowserOrApp()) {
-    return NS_OK;
-  }
-
-  // Only allow content process to embed an app when nested content
-  // process is enabled.
-  if (!XRE_IsParentProcess() &&
-      !(GetBoolAttr(nsGkAtoms::Remote) && NestedEnabled())){
-    NS_WARNING("Can't embed-apps. Embed-apps is restricted to in-proc apps "
-               "or content processes with nested pref enabled, see bug 1097479");
-    return NS_OK;
-  }
-
-  nsAutoString appManifestURL;
-
-  GetManifestURL(appManifestURL);
-
-  bool isApp = !appManifestURL.IsEmpty();
-
-  if (!isApp) {
-    // No valid case to get manifest
-    return NS_OK;
-  }
-
-  if (isApp) {
-    NS_WARNING("Can not simultaneously be mozapp");
-    return NS_OK;
-  }
-
-  nsAutoString manifestURL;
-  if (isApp) {
-    manifestURL.Assign(appManifestURL);
-  }
-
-  aOut.Assign(manifestURL);
-
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsGenericHTMLFrameElement::DisallowCreateFrameLoader()
 {
diff --git a/dom/inputmethod/Keyboard.jsm b/dom/inputmethod/Keyboard.jsm
index 51506c41fa..e110df6fdd 100644
--- a/dom/inputmethod/Keyboard.jsm
+++ b/dom/inputmethod/Keyboard.jsm
@@ -174,8 +174,8 @@ this.Keyboard = {
         this.formMM = null;
       }
     } else {
-      // Ignore notifications that aren't from a BrowserOrApp
-      if (!frameLoader.ownerIsMozBrowserOrAppFrame) {
+      // Ignore notifications that aren't from a Browser
+      if (!frameLoader.ownerIsMozBrowserFrame) {
         return;
       }
       this.initFormsFrameScript(mm);
diff --git a/dom/interfaces/html/nsIMozBrowserFrame.idl b/dom/interfaces/html/nsIMozBrowserFrame.idl
index 99c6cccf63..175f72e985 100644
--- a/dom/interfaces/html/nsIMozBrowserFrame.idl
+++ b/dom/interfaces/html/nsIMozBrowserFrame.idl
@@ -12,44 +12,13 @@ interface nsITabParent;
 interface nsIMozBrowserFrame : nsIDOMMozBrowserFrame
 {
   /**
-   * Gets whether this frame really is a browser or app frame.
+   * Gets whether this frame really is a browser frame.
    *
    * In order to really be a browser frame, this frame's
    * nsIDOMMozBrowserFrame::mozbrowser attribute must be true, and the frame
    * may have to pass various security checks.
    */
-  [infallible] readonly attribute boolean reallyIsBrowserOrApp;
-
-  /**
-   * 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  the frame's mozapp
-   * attribute must point to the manifest of a valid app.
-   */
-  [infallible] readonly attribute boolean reallyIsApp;
-
-  /**
-   * Gets whether this frame is an isolated frame.
-   *
-   * By default, browser frames are isolated, meaning they have a principal
-   * where OriginAttributes.mIsInIsolatedMozBrowser == true.  This isolates
-   * storage and other origin related items from non-browser apps, xul:browsers,
-   * etc.
-   *
-   * Isolation can be disabled by setting the frame's isolated attribute to
-   * false.  Disabling isolation is only allowed if the containing document has
-   * browser permission (or equivalent access).
-   */
-  [infallible] readonly attribute boolean isolated;
-
-  /**
-   * 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.
-   */
-  readonly attribute AString appManifestURL;
+  [infallible] readonly attribute boolean reallyIsBrowser;
 
   /**
    * Normally, a frame tries to create its frame loader when its src is
diff --git a/dom/ipc/ContentBridgeChild.cpp b/dom/ipc/ContentBridgeChild.cpp
index d79ca51d0a..d50f28c1da 100644
--- a/dom/ipc/ContentBridgeChild.cpp
+++ b/dom/ipc/ContentBridgeChild.cpp
@@ -77,7 +77,6 @@ ContentBridgeChild::SendPBrowserConstructor(PBrowserChild* aActor,
                                             const IPCTabContext& aContext,
                                             const uint32_t& aChromeFlags,
                                             const ContentParentId& aCpID,
-                                            const bool& aIsForApp,
                                             const bool& aIsForBrowser)
 {
   return PContentBridgeChild::SendPBrowserConstructor(aActor,
@@ -85,7 +84,6 @@ ContentBridgeChild::SendPBrowserConstructor(PBrowserChild* aActor,
                                                       aContext,
                                                       aChromeFlags,
                                                       aCpID,
-                                                      aIsForApp,
                                                       aIsForBrowser);
 }
 
@@ -130,14 +128,12 @@ ContentBridgeChild::AllocPBrowserChild(const TabId& aTabId,
                                        const IPCTabContext &aContext,
                                        const uint32_t& aChromeFlags,
                                        const ContentParentId& aCpID,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser)
 {
   return nsIContentChild::AllocPBrowserChild(aTabId,
                                              aContext,
                                              aChromeFlags,
                                              aCpID,
-                                             aIsForApp,
                                              aIsForBrowser);
 }
 
@@ -153,7 +149,6 @@ ContentBridgeChild::RecvPBrowserConstructor(PBrowserChild* aActor,
                                             const IPCTabContext& aContext,
                                             const uint32_t& aChromeFlags,
                                             const ContentParentId& aCpID,
-                                            const bool& aIsForApp,
                                             const bool& aIsForBrowser)
 {
   return ContentChild::GetSingleton()->RecvPBrowserConstructor(aActor,
@@ -161,7 +156,6 @@ ContentBridgeChild::RecvPBrowserConstructor(PBrowserChild* aActor,
                                                                aContext,
                                                                aChromeFlags,
                                                                aCpID,
-                                                               aIsForApp,
                                                                aIsForBrowser);
 }
 
diff --git a/dom/ipc/ContentBridgeChild.h b/dom/ipc/ContentBridgeChild.h
index 3b632b806e..c99a134790 100644
--- a/dom/ipc/ContentBridgeChild.h
+++ b/dom/ipc/ContentBridgeChild.h
@@ -42,7 +42,6 @@ public:
                                        const IPCTabContext& aContext,
                                        const uint32_t& aChromeFlags,
                                        const ContentParentId& aCpID,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser) override;
 
   virtual mozilla::ipc::PFileDescriptorSetChild*
@@ -60,7 +59,6 @@ protected:
                                             const IPCTabContext& aContext,
                                             const uint32_t& aChromeFlags,
                                             const ContentParentId& aCpID,
-                                            const bool& aIsForApp,
                                             const bool& aIsForBrowser) override;
   virtual bool DeallocPBrowserChild(PBrowserChild*) override;
   virtual bool RecvPBrowserConstructor(PBrowserChild* aCctor,
@@ -68,7 +66,6 @@ protected:
                                        const IPCTabContext& aContext,
                                        const uint32_t& aChromeFlags,
                                        const ContentParentId& aCpID,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser) override;
 
   virtual mozilla::jsipc::PJavaScriptChild* AllocPJavaScriptChild() override;
diff --git a/dom/ipc/ContentBridgeParent.cpp b/dom/ipc/ContentBridgeParent.cpp
index 973da94ce0..c7e3b1609c 100644
--- a/dom/ipc/ContentBridgeParent.cpp
+++ b/dom/ipc/ContentBridgeParent.cpp
@@ -102,7 +102,6 @@ ContentBridgeParent::SendPBrowserConstructor(PBrowserParent* aActor,
                                              const IPCTabContext& aContext,
                                              const uint32_t& aChromeFlags,
                                              const ContentParentId& aCpID,
-                                             const bool& aIsForApp,
                                              const bool& aIsForBrowser)
 {
   return PContentBridgeParent::SendPBrowserConstructor(aActor,
@@ -110,7 +109,6 @@ ContentBridgeParent::SendPBrowserConstructor(PBrowserParent* aActor,
                                                        aContext,
                                                        aChromeFlags,
                                                        aCpID,
-                                                       aIsForApp,
                                                        aIsForBrowser);
 }
 
@@ -143,14 +141,12 @@ ContentBridgeParent::AllocPBrowserParent(const TabId& aTabId,
                                          const IPCTabContext &aContext,
                                          const uint32_t& aChromeFlags,
                                          const ContentParentId& aCpID,
-                                         const bool& aIsForApp,
                                          const bool& aIsForBrowser)
 {
   return nsIContentParent::AllocPBrowserParent(aTabId,
                                                aContext,
                                                aChromeFlags,
                                                aCpID,
-                                               aIsForApp,
                                                aIsForBrowser);
 }
 
diff --git a/dom/ipc/ContentBridgeParent.h b/dom/ipc/ContentBridgeParent.h
index f79ea453ff..27c7041a2b 100644
--- a/dom/ipc/ContentBridgeParent.h
+++ b/dom/ipc/ContentBridgeParent.h
@@ -42,7 +42,6 @@ public:
                           const IPCTabContext& aContext,
                           const uint32_t& aChromeFlags,
                           const ContentParentId& aCpID,
-                          const bool& aIsForApp,
                           const bool& aIsForBrowser) override;
 
   FORWARD_SHMEM_ALLOCATOR_TO(PContentBridgeParent)
@@ -53,10 +52,6 @@ public:
   {
     return mChildID;
   }
-  virtual bool IsForApp() const override
-  {
-    return mIsForApp;
-  }
   virtual bool IsForBrowser() const override
   {
     return mIsForBrowser;
@@ -75,11 +70,6 @@ protected:
     mChildID = aId;
   }
 
-  void SetIsForApp(bool aIsForApp)
-  {
-    mIsForApp = aIsForApp;
-  }
-
   void SetIsForBrowser(bool aIsForBrowser)
   {
     mIsForBrowser = aIsForBrowser;
@@ -114,7 +104,6 @@ protected:
                       const IPCTabContext &aContext,
                       const uint32_t& aChromeFlags,
                       const ContentParentId& aCpID,
-                      const bool& aIsForApp,
                       const bool& aIsForBrowser) override;
 
   virtual bool DeallocPBrowserParent(PBrowserParent*) override;
@@ -140,7 +129,6 @@ protected: // members
   RefPtr<ContentBridgeParent> mSelfRef;
   Transport* mTransport; // owned
   ContentParentId mChildID;
-  bool mIsForApp;
   bool mIsForBrowser;
 
 private:
diff --git a/dom/ipc/ContentChild.cpp b/dom/ipc/ContentChild.cpp
index 8e7df1e288..1d82a4852f 100644
--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -556,7 +556,7 @@ ContentChild::Init(MessageLoop* aIOLoop,
   SendBackUpXResources(FileDescriptor(xSocketFd));
 #endif
 
-  SendGetProcessAttributes(&mID, &mIsForApp, &mIsForBrowser);
+  SendGetProcessAttributes(&mID, &mIsForBrowser);
   InitProcessAttributes();
 
 #ifdef NS_PRINTING
@@ -680,7 +680,7 @@ ContentChild::ProvideWindowCommon(TabChild* aTabOpener,
     // We release this ref in DeallocPBrowserChild
     RefPtr<TabChild>(newChild).forget().take(),
     tabId, *ipcContext, aChromeFlags,
-    GetID(), IsForApp(), IsForBrowser());
+    GetID(), IsForBrowser());
 
   nsString name(aName);
   nsAutoCString features(aFeatures);
@@ -1273,14 +1273,12 @@ ContentChild::AllocPBrowserChild(const TabId& aTabId,
                                  const IPCTabContext& aContext,
                                  const uint32_t& aChromeFlags,
                                  const ContentParentId& aCpID,
-                                 const bool& aIsForApp,
                                  const bool& aIsForBrowser)
 {
   return nsIContentChild::AllocPBrowserChild(aTabId,
                                              aContext,
                                              aChromeFlags,
                                              aCpID,
-                                             aIsForApp,
                                              aIsForBrowser);
 }
 
@@ -1290,7 +1288,6 @@ ContentChild::SendPBrowserConstructor(PBrowserChild* aActor,
                                       const IPCTabContext& aContext,
                                       const uint32_t& aChromeFlags,
                                       const ContentParentId& aCpID,
-                                      const bool& aIsForApp,
                                       const bool& aIsForBrowser)
 {
   if (IsShuttingDown()) {
@@ -1302,7 +1299,6 @@ ContentChild::SendPBrowserConstructor(PBrowserChild* aActor,
                                                 aContext,
                                                 aChromeFlags,
                                                 aCpID,
-                                                aIsForApp,
                                                 aIsForBrowser);
 }
 
@@ -1312,7 +1308,6 @@ ContentChild::RecvPBrowserConstructor(PBrowserChild* aActor,
                                       const IPCTabContext& aContext,
                                       const uint32_t& aChromeFlags,
                                       const ContentParentId& aCpID,
-                                      const bool& aIsForApp,
                                       const bool& aIsForBrowser)
 {
   MOZ_ASSERT(!IsShuttingDown());
@@ -1339,7 +1334,6 @@ ContentChild::RecvPBrowserConstructor(PBrowserChild* aActor,
     // Redo InitProcessAttributes() when the app or browser is really
     // launching so the attributes will be correct.
     mID = aCpID;
-    mIsForApp = aIsForApp;
     mIsForBrowser = aIsForBrowser;
     InitProcessAttributes();
   }
@@ -2125,7 +2119,7 @@ ContentChild::RecvAppInit()
   // PreloadSlowThings() may set the docshell of the first TabChild
   // inactive, and we can only safely restore it to active from
   // BrowserElementChild.js.
-  if (mIsForApp || mIsForBrowser) {
+  if (mIsForBrowser) {
     PreloadSlowThings();
   }
 
diff --git a/dom/ipc/ContentChild.h b/dom/ipc/ContentChild.h
index e0b03d62fd..46e9febe24 100644
--- a/dom/ipc/ContentChild.h
+++ b/dom/ipc/ContentChild.h
@@ -175,7 +175,6 @@ public:
                                             const IPCTabContext& aContext,
                                             const uint32_t& aChromeFlags,
                                             const ContentParentId& aCpID,
-                                            const bool& aIsForApp,
                                             const bool& aIsForBrowser) override;
 
   virtual bool DeallocPBrowserChild(PBrowserChild*) override;
@@ -483,7 +482,6 @@ public:
   uint32_t GetMsaaID() const { return mMsaaID; }
 #endif
 
-  bool IsForApp() const { return mIsForApp; }
   bool IsForBrowser() const { return mIsForBrowser; }
 
   virtual PBlobChild*
@@ -504,7 +502,6 @@ public:
                                        const IPCTabContext& context,
                                        const uint32_t& chromeFlags,
                                        const ContentParentId& aCpID,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser) override;
 
   virtual bool RecvPBrowserConstructor(PBrowserChild* aCctor,
@@ -512,7 +509,6 @@ public:
                                        const IPCTabContext& aContext,
                                        const uint32_t& aChromeFlags,
                                        const ContentParentId& aCpID,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser) override;
 
   FORWARD_SHMEM_ALLOCATOR_TO(PContentChild)
@@ -618,7 +614,6 @@ private:
 
   AppInfo mAppInfo;
 
-  bool mIsForApp;
   bool mIsForBrowser;
   bool mCanOverrideProcessName;
   bool mIsAlive;
diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 3fc86f5b6b..0261950822 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -27,7 +27,6 @@
 #include "HandlerServiceParent.h"
 #include "IHistory.h"
 #include "imgIContainer.h"
-#include "mozIApplication.h"
 #if defined(XP_WIN) && defined(ACCESSIBILITY)
 #include "mozilla/a11y/AccessibleWrap.h"
 #endif
@@ -460,8 +459,7 @@ ContentParentsMemoryReporter::CollectReports(
   return NS_OK;
 }
 
-nsDataHashtable<nsStringHashKey, ContentParent*>* ContentParent::sAppContentParents;
-nsTArray<ContentParent*>* ContentParent::sNonAppContentParents;
+nsTArray<ContentParent*>* ContentParent::sBrowserContentParents;
 nsTArray<ContentParent*>* ContentParent::sLargeAllocationContentParents;
 nsTArray<ContentParent*>* ContentParent::sPrivateContent;
 StaticAutoPtr<LinkedList<ContentParent> > ContentParent::sContentParents;
@@ -477,11 +475,6 @@ static bool sDisableUnsafeCPOWWarnings = false;
 // The first content child has ID 1, so the chrome process can have ID 0.
 static uint64_t gContentChildID = 1;
 
-// We want the prelaunched process to know that it's for apps, but not
-// actually for any app in particular.  Use a magic manifest URL.
-// Can't be a static constant.
-#define MAGIC_PREALLOCATED_APP_MANIFEST_URL NS_LITERAL_STRING("{{template}}")
-
 static const char* sObserverTopics[] = {
   "xpcom-shutdown",
   "profile-before-change",
@@ -507,8 +500,7 @@ static const char* sObserverTopics[] = {
 ContentParent::PreallocateAppProcess()
 {
   RefPtr<ContentParent> process =
-    new ContentParent(/* app = */ nullptr,
-                      /* aOpener = */ nullptr,
+    new ContentParent(/* aOpener = */ nullptr,
                       /* isForBrowserElement = */ false,
                       /* isForPreallocated = */ true);
 
@@ -520,57 +512,6 @@ ContentParent::PreallocateAppProcess()
   return process.forget();
 }
 
-/*static*/ already_AddRefed<ContentParent>
-ContentParent::GetNewOrPreallocatedAppProcess(mozIApplication* aApp,
-                                              ProcessPriority aInitialPriority,
-                                              ContentParent* aOpener,
-                                              /*out*/ bool* aTookPreAllocated)
-{
-  MOZ_ASSERT(aApp);
-  RefPtr<ContentParent> process = PreallocatedProcessManager::Take();
-
-  if (process) {
-    if (!process->SetPriorityAndCheckIsAlive(aInitialPriority)) {
-      // Kill the process just in case it's not actually dead; we don't want
-      // to "leak" this process!
-      process->KillHard("GetNewOrPreallocatedAppProcess");
-    }
-    else {
-      nsAutoString manifestURL;
-      if (NS_FAILED(aApp->GetManifestURL(manifestURL))) {
-        NS_ERROR("Failed to get manifest URL");
-        return nullptr;
-      }
-      process->TransformPreallocatedIntoApp(aOpener, manifestURL);
-      process->ForwardKnownInfo();
-
-      if (aTookPreAllocated) {
-        *aTookPreAllocated = true;
-      }
-      return process.forget();
-    }
-  }
-
-  NS_WARNING("Unable to use pre-allocated app process");
-  process = new ContentParent(aApp,
-                              /* aOpener = */ aOpener,
-                              /* isForBrowserElement = */ false,
-                              /* isForPreallocated = */ false);
-
-  if (!process->LaunchSubprocess(aInitialPriority)) {
-    return nullptr;
-  }
-
-  process->Init();
-  process->ForwardKnownInfo();
-
-  if (aTookPreAllocated) {
-    *aTookPreAllocated = false;
-  }
-
-  return process.forget();
-}
-
 /*static*/ void
 ContentParent::StartUp()
 {
@@ -672,10 +613,10 @@ ContentParent::GetNewOrUsedBrowserProcess(bool aForBrowserElement,
 
     maxContentParents = Preferences::GetInt("dom.ipc.dedicatedProcessCount", 2);
   } else {
-    if (!sNonAppContentParents) {
-      sNonAppContentParents = new nsTArray<ContentParent*>();
+    if (!sBrowserContentParents) {
+      sBrowserContentParents = new nsTArray<ContentParent*>();
     }
-    contentParents = sNonAppContentParents;
+    contentParents = sBrowserContentParents;
 
     maxContentParents = Preferences::GetInt("dom.ipc.processCount", 1);
   }
@@ -691,7 +632,7 @@ ContentParent::GetNewOrUsedBrowserProcess(bool aForBrowserElement,
     uint32_t currIdx = startIdx;
     do {
       RefPtr<ContentParent> p = (*contentParents)[currIdx];
-      NS_ASSERTION(p->IsAlive(), "Non-alive contentparent in sNonAppContntParents?");
+      NS_ASSERTION(p->IsAlive(), "Non-alive contentparent in sBrowserContntParents?");
       if (p->mOpener == aOpener) {
         return p.forget();
       }
@@ -705,8 +646,7 @@ ContentParent::GetNewOrUsedBrowserProcess(bool aForBrowserElement,
     p->TransformPreallocatedIntoBrowser(aOpener);
   } else {
     // Failed in using the preallocated process: fork from the chrome process.
-    p = new ContentParent(/* app = */ nullptr,
-                          aOpener,
+    p = new ContentParent(aOpener,
                           aForBrowserElement,
                           /* isForPreallocated = */ false);
 
@@ -782,7 +722,6 @@ ContentParent::RecvCreateChildProcess(const IPCTabContext& aContext,
                                       const hal::ProcessPriority& aPriority,
                                       const TabId& aOpenerTabId,
                                       ContentParentId* aCpId,
-                                      bool* aIsForApp,
                                       bool* aIsForBrowser,
                                       TabId* aTabId)
 {
@@ -800,24 +739,16 @@ ContentParent::RecvCreateChildProcess(const IPCTabContext& aContext,
     return false;
   }
 
-  nsCOMPtr<mozIApplication> ownApp = tc.GetTabContext().GetOwnApp();
-  if (ownApp) {
-    cp = GetNewOrPreallocatedAppProcess(ownApp, aPriority, this);
-  }
-  else {
-   cp = GetNewOrUsedBrowserProcess(/* isBrowserElement = */ true,
-                                   aPriority, this);
-  }
+  cp = GetNewOrUsedBrowserProcess(/* isBrowserElement = */ true,
+                                  aPriority, this);
 
   if (!cp) {
     *aCpId = 0;
-    *aIsForApp = false;
     *aIsForBrowser = false;
     return true;
   }
 
   *aCpId = cp->ChildID();
-  *aIsForApp = cp->IsForApp();
   *aIsForBrowser = cp->IsForBrowser();
 
   ContentProcessManager *cpm = ContentProcessManager::GetSingleton();
@@ -950,10 +881,10 @@ ContentParent::RecvFindPlugins(const uint32_t& aPluginEpoch,
 }
 
 /*static*/ TabParent*
-ContentParent::CreateBrowserOrApp(const TabContext& aContext,
-                                  Element* aFrameElement,
-                                  ContentParent* aOpenerContentParent,
-                                  bool aFreshProcess)
+ContentParent::CreateBrowser(const TabContext& aContext,
+                             Element* aFrameElement,
+                             ContentParent* aOpenerContentParent,
+                             bool aFreshProcess)
 {
   PROFILER_LABEL_FUNC(js::ProfileEntry::Category::OTHER);
 
@@ -976,222 +907,74 @@ ContentParent::CreateBrowserOrApp(const TabContext& aContext,
     openerTabId = TabParent::GetTabIdFrom(docShell);
   }
 
-  if (aContext.IsMozBrowserElement() || !aContext.HasOwnApp()) {
-    RefPtr<nsIContentParent> constructorSender;
-    if (isInContentProcess) {
-      MOZ_ASSERT(aContext.IsMozBrowserElement());
-      constructorSender = CreateContentBridgeParent(aContext, initialPriority,
-                                                    openerTabId, &tabId);
-    } else {
-      if (aOpenerContentParent) {
-        constructorSender = aOpenerContentParent;
-      } else {
-        constructorSender =
-          GetNewOrUsedBrowserProcess(aContext.IsMozBrowserElement(),
-                                     initialPriority,
-                                     nullptr,
-                                     aFreshProcess);
-        if (!constructorSender) {
-          return nullptr;
-        }
-      }
-      tabId = AllocateTabId(openerTabId,
-                            aContext.AsIPCTabContext(),
-                            constructorSender->ChildID());
-    }
-    if (constructorSender) {
-      nsCOMPtr<nsIDocShellTreeOwner> treeOwner;
-      docShell->GetTreeOwner(getter_AddRefs(treeOwner));
-      if (!treeOwner) {
-        return nullptr;
-      }
-
-      nsCOMPtr<nsIWebBrowserChrome> wbc = do_GetInterface(treeOwner);
-      if (!wbc) {
-        return nullptr;
-      }
-      uint32_t chromeFlags = 0;
-      wbc->GetChromeFlags(&chromeFlags);
-
-      nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(docShell);
-      if (loadContext && loadContext->UsePrivateBrowsing()) {
-        chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW;
-      }
-      if (docShell->GetAffectPrivateSessionLifetime()) {
-        chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_LIFETIME;
-      }
-
-      if (tabId == 0) {
-        return nullptr;
-      }
-      RefPtr<TabParent> tp(new TabParent(constructorSender, tabId,
-                                         aContext, chromeFlags));
-      tp->SetInitedByParent();
-
-      PBrowserParent* browser =
-      constructorSender->SendPBrowserConstructor(
-        // DeallocPBrowserParent() releases this ref.
-        tp.forget().take(), tabId,
-        aContext.AsIPCTabContext(),
-        chromeFlags,
-        constructorSender->ChildID(),
-        constructorSender->IsForApp(),
-        constructorSender->IsForBrowser());
-
-      if (aFreshProcess) {
-        Unused << browser->SendSetFreshProcess();
-      }
-
-      if (browser) {
-        RefPtr<TabParent> constructedTabParent = TabParent::GetFrom(browser);
-        constructedTabParent->SetOwnerElement(aFrameElement);
-        return constructedTabParent;
-      }
-    }
-    return nullptr;
-  }
-
-  // If we got here, we have an app and we're not a browser element.  ownApp
-  // shouldn't be null, because we otherwise would have gone into the
-  // !HasOwnApp() branch above.
-  RefPtr<nsIContentParent> parent;
-  bool reused = false;
-  bool tookPreallocated = false;
-  nsAutoString manifestURL;
-
+  RefPtr<nsIContentParent> constructorSender;
   if (isInContentProcess) {
-    parent = CreateContentBridgeParent(aContext,
-                                       initialPriority,
-                                       openerTabId,
-                                       &tabId);
-  }
-  else {
-    nsCOMPtr<mozIApplication> ownApp = aContext.GetOwnApp();
-
-    if (!sAppContentParents) {
-      sAppContentParents =
-        new nsDataHashtable<nsStringHashKey, ContentParent*>();
+    MOZ_ASSERT(aContext.IsMozBrowserElement());
+    constructorSender = CreateContentBridgeParent(aContext, initialPriority,
+                                                  openerTabId, &tabId);
+  } else {
+    constructorSender =
+      GetNewOrUsedBrowserProcess(aContext.IsMozBrowserElement(),
+                                 initialPriority, nullptr, aFreshProcess);
+    if (!constructorSender) {
+      return nullptr;
     }
+    tabId = AllocateTabId(openerTabId,
+                          aContext.AsIPCTabContext(),
+                          constructorSender->ChildID());
+  }
 
-    // Each app gets its own ContentParent instance unless it shares it with
-    // a parent app.
-    if (NS_FAILED(ownApp->GetManifestURL(manifestURL))) {
-      NS_ERROR("Failed to get manifest URL");
+  if (constructorSender) {
+    nsCOMPtr<nsIDocShellTreeOwner> treeOwner;
+    docShell->GetTreeOwner(getter_AddRefs(treeOwner));
+    if (!treeOwner) {
       return nullptr;
     }
 
-    RefPtr<ContentParent> p = sAppContentParents->Get(manifestURL);
-
-    if (!p && Preferences::GetBool("dom.ipc.reuse_parent_app")) {
-      nsAutoString parentAppManifestURL;
-      aFrameElement->GetAttr(kNameSpaceID_None,
-                             nsGkAtoms::parentapp, parentAppManifestURL);
-      nsAdoptingString systemAppManifestURL =
-        Preferences::GetString("b2g.system_manifest_url");
-      nsCOMPtr<nsIAppsService> appsService =
-        do_GetService(APPS_SERVICE_CONTRACTID);
-      if (!parentAppManifestURL.IsEmpty() &&
-        !parentAppManifestURL.Equals(systemAppManifestURL) &&
-        appsService) {
-        nsCOMPtr<mozIApplication> parentApp;
-        nsCOMPtr<mozIApplication> app;
-        appsService->GetAppByManifestURL(parentAppManifestURL,
-                                         getter_AddRefs(parentApp));
-        appsService->GetAppByManifestURL(manifestURL,
-                                         getter_AddRefs(app));
-
-        // Only let certified apps re-use the same process.
-        unsigned short parentAppStatus = 0;
-        unsigned short appStatus = 0;
-        if (app &&
-          NS_SUCCEEDED(app->GetAppStatus(&appStatus)) &&
-          appStatus == nsIPrincipal::APP_STATUS_CERTIFIED &&
-          parentApp &&
-          NS_SUCCEEDED(parentApp->GetAppStatus(&parentAppStatus)) &&
-          parentAppStatus == nsIPrincipal::APP_STATUS_CERTIFIED) {
-          // Check if we can re-use the process of the parent app.
-          p = sAppContentParents->Get(parentAppManifestURL);
-        }
-      }
+    nsCOMPtr<nsIWebBrowserChrome> wbc = do_GetInterface(treeOwner);
+    if (!wbc) {
+      return nullptr;
     }
 
-    if (p) {
-      // Check that the process is still alive and set its priority.
-      // Hopefully the process won't die after this point, if this call
-      // succeeds.
-      if (!p->SetPriorityAndCheckIsAlive(initialPriority)) {
-        p = nullptr;
-      }
+    uint32_t chromeFlags = 0;
+    wbc->GetChromeFlags(&chromeFlags);
+
+    nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(docShell);
+    if (loadContext && loadContext->UsePrivateBrowsing()) {
+      chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_WINDOW;
     }
 
-    reused = !!p;
-    if (!p) {
-      p = GetNewOrPreallocatedAppProcess(ownApp, initialPriority, nullptr,
-                                         &tookPreallocated);
-      MOZ_ASSERT(p);
-      sAppContentParents->Put(manifestURL, p);
-    }
-    tabId = AllocateTabId(openerTabId, aContext.AsIPCTabContext(),
-                          p->ChildID());
-    parent = static_cast<nsIContentParent*>(p);
-  }
-
-  if (!parent || (tabId == 0)) {
-    return nullptr;
-  }
-
-  uint32_t chromeFlags = 0;
-
-  RefPtr<TabParent> tp = new TabParent(parent, tabId, aContext, chromeFlags);
-  tp->SetInitedByParent();
-  PBrowserParent* browser = parent->SendPBrowserConstructor(
-    // DeallocPBrowserParent() releases this ref.
-    RefPtr<TabParent>(tp).forget().take(),
-    tabId,
-    aContext.AsIPCTabContext(),
-    chromeFlags,
-    parent->ChildID(),
-    parent->IsForApp(),
-    parent->IsForBrowser());
-
-  if (aFreshProcess) {
-    Unused << browser->SendSetFreshProcess();
-  }
-
-  if (browser) {
-    RefPtr<TabParent> constructedTabParent = TabParent::GetFrom(browser);
-    constructedTabParent->SetOwnerElement(aFrameElement);
-  }
-
-  if (isInContentProcess) {
-    // Just return directly without the following check in content process.
-    return TabParent::GetFrom(browser);
-  }
-
-  if (!browser) {
-    // We failed to actually start the PBrowser.  This can happen if the
-    // other process has already died.
-    if (!reused) {
-      // Don't leave a broken ContentParent in the hashtable.
-      parent->AsContentParent()->KillHard("CreateBrowserOrApp");
-      sAppContentParents->Remove(manifestURL);
-      parent = nullptr;
+    if (docShell->GetAffectPrivateSessionLifetime()) {
+      chromeFlags |= nsIWebBrowserChrome::CHROME_PRIVATE_LIFETIME;
     }
 
-    // If we took the preallocated process and it was already dead, try
-    // again with a non-preallocated process.  We can be sure this won't
-    // loop forever, because the next time through there will be no
-    // preallocated process to take.
-    if (tookPreallocated) {
-      return ContentParent::CreateBrowserOrApp(aContext, aFrameElement,
-                                               aOpenerContentParent);
+    if (tabId == 0) {
+      return nullptr;
+    }
+    RefPtr<TabParent> tp(new TabParent(constructorSender, tabId,
+                                       aContext, chromeFlags));
+    tp->SetInitedByParent();
+
+    PBrowserParent* browser =
+    constructorSender->SendPBrowserConstructor(
+      // DeallocPBrowserParent() releases this ref.
+      tp.forget().take(), tabId,
+      aContext.AsIPCTabContext(),
+      chromeFlags,
+      constructorSender->ChildID(),
+      constructorSender->IsForBrowser());
+
+    if (aFreshProcess) {
+      Unused << browser->SendSetFreshProcess();
     }
 
-    // Otherwise just give up.
-    return nullptr;
+    if (browser) {
+      RefPtr<TabParent> constructedTabParent = TabParent::GetFrom(browser);
+      constructedTabParent->SetOwnerElement(aFrameElement);
+      return constructedTabParent;
+    }
   }
-
-  return TabParent::GetFrom(browser);
+  return nullptr;
 }
 
 /*static*/ ContentBridgeParent*
@@ -1204,13 +987,11 @@ ContentParent::CreateContentBridgeParent(const TabContext& aContext,
 
   ContentChild* child = ContentChild::GetSingleton();
   ContentParentId cpId;
-  bool isForApp;
   bool isForBrowser;
   if (!child->SendCreateChildProcess(aContext.AsIPCTabContext(),
                                      aPriority,
                                      aOpenerTabId,
                                      &cpId,
-                                     &isForApp,
                                      &isForBrowser,
                                      aTabId)) {
     return nullptr;
@@ -1223,7 +1004,6 @@ ContentParent::CreateContentBridgeParent(const TabContext& aContext,
   }
   ContentBridgeParent* parent = child->GetLastBridge();
   parent->SetChildID(cpId);
-  parent->SetIsForApp(isForApp);
   parent->SetIsForBrowser(isForBrowser);
   return parent;
 }
@@ -1344,48 +1124,12 @@ ContentParent::SetPriorityAndCheckIsAlive(ProcessPriority aPriority)
   return true;
 }
 
-// Helper for ContentParent::TransformPreallocatedIntoApp.
-static void
-TryGetNameFromManifestURL(const nsAString& aManifestURL,
-              nsAString& aName)
-{
-  aName.Truncate();
-  if (aManifestURL.IsEmpty() ||
-    aManifestURL == MAGIC_PREALLOCATED_APP_MANIFEST_URL) {
-    return;
-  }
-
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  NS_ENSURE_TRUE_VOID(appsService);
-
-  nsCOMPtr<mozIApplication> app;
-  appsService->GetAppByManifestURL(aManifestURL, getter_AddRefs(app));
-
-  if (!app) {
-    return;
-  }
-
-  app->GetName(aName);
-}
-
-void
-ContentParent::TransformPreallocatedIntoApp(ContentParent* aOpener,
-                                            const nsAString& aAppManifestURL)
-{
-  MOZ_ASSERT(IsPreallocated());
-  mMetamorphosed = true;
-  mOpener = aOpener;
-  mAppManifestURL = aAppManifestURL;
-  TryGetNameFromManifestURL(aAppManifestURL, mAppName);
-}
-
 void
 ContentParent::TransformPreallocatedIntoBrowser(ContentParent* aOpener)
 {
-  // Reset mAppManifestURL, mIsForBrowser and mOSPrivileges for browser.
+  // Reset mIsForBrowser and mOSPrivileges for browser.
   mMetamorphosed = true;
   mOpener = aOpener;
-  mAppManifestURL.Truncate();
   mIsForBrowser = true;
 }
 
@@ -1472,29 +1216,19 @@ ContentParent::ShutDownMessageManager()
 void
 ContentParent::MarkAsDead()
 {
-  if (!mAppManifestURL.IsEmpty()) {
-    if (sAppContentParents) {
-      sAppContentParents->Remove(mAppManifestURL);
-      if (!sAppContentParents->Count()) {
-        delete sAppContentParents;
-        sAppContentParents = nullptr;
-      }
-    }
-  } else {
-    if (sNonAppContentParents) {
-      sNonAppContentParents->RemoveElement(this);
-      if (!sNonAppContentParents->Length()) {
-        delete sNonAppContentParents;
-        sNonAppContentParents = nullptr;
-      }
+  if (sBrowserContentParents) {
+    sBrowserContentParents->RemoveElement(this);
+    if (!sBrowserContentParents->Length()) {
+      delete sBrowserContentParents;
+      sBrowserContentParents = nullptr;
     }
+  }
 
-    if (sLargeAllocationContentParents) {
-      sLargeAllocationContentParents->RemoveElement(this);
-      if (!sLargeAllocationContentParents->Length()) {
-        delete sLargeAllocationContentParents;
-        sLargeAllocationContentParents = nullptr;
-      }
+  if (sLargeAllocationContentParents) {
+    sLargeAllocationContentParents->RemoveElement(this);
+    if (!sLargeAllocationContentParents->Length()) {
+      delete sLargeAllocationContentParents;
+      sLargeAllocationContentParents = nullptr;
     }
   }
 
@@ -1797,7 +1531,7 @@ ContentParent::NotifyTabDestroying(const TabId& aTabId,
         return;
     }
 
-    uint32_t numberOfParents = sNonAppContentParents ? sNonAppContentParents->Length() : 0;
+    uint32_t numberOfParents = sBrowserContentParents ? sBrowserContentParents->Length() : 0;
     int32_t processesToKeepAlive = Preferences::GetInt("dom.ipc.keepProcessesAlive", 0);
     if (!cp->mLargeAllocationProcess && static_cast<int32_t>(numberOfParents) <= processesToKeepAlive) {
       return;
@@ -1854,7 +1588,7 @@ ContentParent::NotifyTabDestroyed(const TabId& aTabId,
 
   // We might want to keep alive some content processes for testing, because of performance
   // reasons, but we don't want to alter behavior if the pref is not set.
-  uint32_t numberOfParents = sNonAppContentParents ? sNonAppContentParents->Length() : 0;
+  uint32_t numberOfParents = sBrowserContentParents ? sBrowserContentParents->Length() : 0;
   int32_t processesToKeepAlive = Preferences::GetInt("dom.ipc.keepProcessesAlive", 0);
   bool shouldKeepAliveAny = !mLargeAllocationProcess && processesToKeepAlive > 0;
   bool shouldKeepAliveThis = shouldKeepAliveAny && static_cast<int32_t>(numberOfParents) <= processesToKeepAlive;
@@ -1948,20 +1682,20 @@ ContentParent::LaunchSubprocess(ProcessPriority aInitialPriority /* = PROCESS_PR
   return true;
 }
 
-ContentParent::ContentParent(mozIApplication* aApp,
-                             ContentParent* aOpener,
+ContentParent::ContentParent(ContentParent* aOpener,
                              bool aIsForBrowser,
                              bool aIsForPreallocated)
   : nsIContentParent()
   , mOpener(aOpener)
   , mIsForBrowser(aIsForBrowser)
+  , mIsPreallocated(aIsForPreallocated)
   , mLargeAllocationProcess(false)
 {
   InitializeMembers();  // Perform common initialization.
 
-  // No more than one of !!aApp, aIsForBrowser, aIsForPreallocated should be
+  // No more than one of aIsForBrowser, aIsForPreallocated should be
   // true.
-  MOZ_ASSERT(!!aApp + aIsForBrowser + aIsForPreallocated <= 1);
+  MOZ_ASSERT(aIsForBrowser + aIsForPreallocated <= 1);
 
   mMetamorphosed = true;
 
@@ -1971,13 +1705,6 @@ ContentParent::ContentParent(mozIApplication* aApp,
   }
   sContentParents->insertBack(this);
 
-  if (aApp) {
-    aApp->GetManifestURL(mAppManifestURL);
-    aApp->GetName(mAppName);
-  } else if (aIsForPreallocated) {
-    mAppManifestURL = MAGIC_PREALLOCATED_APP_MANIFEST_URL;
-  }
-
   // From this point on, NS_WARNING, NS_ASSERTION, etc. should print out the
   // PID along with the warning.
   nsDebugImpl::SetMultiprocessMode("Parent");
@@ -2004,19 +1731,10 @@ ContentParent::~ContentParent()
 
   // We should be removed from all these lists in ActorDestroy.
   MOZ_ASSERT(!sPrivateContent || !sPrivateContent->Contains(this));
-  if (mAppManifestURL.IsEmpty()) {
-    MOZ_ASSERT((!sNonAppContentParents ||
-                !sNonAppContentParents->Contains(this)) &&
-               (!sLargeAllocationContentParents ||
-                !sLargeAllocationContentParents->Contains(this)));
-  } else {
-    // In general, we expect sAppContentParents->Get(mAppManifestURL) to be
-    // nullptr.  But it could be that we created another ContentParent for
-    // this app after we did this->ActorDestroy(), so the right check is
-    // that sAppContentParents->Get(mAppManifestURL) != this.
-    MOZ_ASSERT(!sAppContentParents ||
-               sAppContentParents->Get(mAppManifestURL) != this);
-  }
+  MOZ_ASSERT((!sBrowserContentParents ||
+              !sBrowserContentParents->Contains(this)) &&
+             (!sLargeAllocationContentParents ||
+              !sLargeAllocationContentParents->Contains(this)));
 }
 
 void
@@ -2152,12 +1870,6 @@ ContentParent::IsAlive() const
   return mIsAlive;
 }
 
-bool
-ContentParent::IsForApp() const
-{
-  return !mAppManifestURL.IsEmpty();
-}
-
 int32_t
 ContentParent::Pid() const
 {
@@ -2585,10 +2297,9 @@ ContentParent::AllocPProcessHangMonitorParent(Transport* aTransport,
 
 bool
 ContentParent::RecvGetProcessAttributes(ContentParentId* aCpId,
-                                        bool* aIsForApp, bool* aIsForBrowser)
+                                        bool* aIsForBrowser)
 {
   *aCpId = mChildID;
-  *aIsForApp = IsForApp();
   *aIsForBrowser = mIsForBrowser;
 
   return true;
@@ -2697,14 +2408,12 @@ ContentParent::AllocPBrowserParent(const TabId& aTabId,
                                    const IPCTabContext& aContext,
                                    const uint32_t& aChromeFlags,
                                    const ContentParentId& aCpId,
-                                   const bool& aIsForApp,
                                    const bool& aIsForBrowser)
 {
   return nsIContentParent::AllocPBrowserParent(aTabId,
                                                aContext,
                                                aChromeFlags,
                                                aCpId,
-                                               aIsForApp,
                                                aIsForBrowser);
 }
 
@@ -2805,7 +2514,7 @@ ContentParent::KillHard(const char* aReason)
 bool
 ContentParent::IsPreallocated() const
 {
-  return mAppManifestURL == MAGIC_PREALLOCATED_APP_MANIFEST_URL;
+  return mIsPreallocated;
 }
 
 void
@@ -2818,11 +2527,6 @@ ContentParent::FriendlyName(nsAString& aName, bool aAnonymize)
     aName.AssignLiteral("Browser");
   } else if (aAnonymize) {
     aName.AssignLiteral("<anonymized-name>");
-  } else if (!mAppName.IsEmpty()) {
-    aName = mAppName;
-  } else if (!mAppManifestURL.IsEmpty()) {
-    aName.AssignLiteral("Unknown app: ");
-    aName.Append(mAppManifestURL);
   } else {
     aName.AssignLiteral("???");
   }
@@ -3659,7 +3363,6 @@ ContentParent::SendPBrowserConstructor(PBrowserParent* aActor,
                                        const IPCTabContext& aContext,
                                        const uint32_t& aChromeFlags,
                                        const ContentParentId& aCpId,
-                                       const bool& aIsForApp,
                                        const bool& aIsForBrowser)
 {
   return PContentParent::SendPBrowserConstructor(aActor,
@@ -3667,7 +3370,6 @@ ContentParent::SendPBrowserConstructor(PBrowserParent* aActor,
                                                  aContext,
                                                  aChromeFlags,
                                                  aCpId,
-                                                 aIsForApp,
                                                  aIsForBrowser);
 }
 
@@ -3785,12 +3487,9 @@ ContentParent::RecvRecordingDeviceEvents(const nsString& aRecordingStatus,
     // recording-device-ipc-events needs to gather more information from content process
     RefPtr<nsHashPropertyBag> props = new nsHashPropertyBag();
     props->SetPropertyAsUint64(NS_LITERAL_STRING("childID"), ChildID());
-    props->SetPropertyAsBool(NS_LITERAL_STRING("isApp"), IsForApp());
     props->SetPropertyAsBool(NS_LITERAL_STRING("isAudio"), aIsAudio);
     props->SetPropertyAsBool(NS_LITERAL_STRING("isVideo"), aIsVideo);
-
-    nsString requestURL = IsForApp() ? AppManifestURL() : aPageURL;
-    props->SetPropertyAsAString(NS_LITERAL_STRING("requestURL"), requestURL);
+    props->SetPropertyAsAString(NS_LITERAL_STRING("requestURL"), aPageURL);
 
     obs->NotifyObservers((nsIPropertyBag2*) props,
                          "recording-device-ipc-events",
@@ -4245,7 +3944,7 @@ ContentParent::RecvCreateWindow(PBrowserParent* aThisTab,
     thisTabParent = TabParent::GetFrom(aThisTab);
   }
 
-  if (NS_WARN_IF(thisTabParent && thisTabParent->IsMozBrowserOrApp())) {
+  if (NS_WARN_IF(thisTabParent && thisTabParent->IsMozBrowser())) {
     return false;
   }
 
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index 15f29dbbc6..e8e7c86c3b 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -140,10 +140,10 @@ public:
    * associated.
    */
   static TabParent*
-  CreateBrowserOrApp(const TabContext& aContext,
-                     Element* aFrameElement,
-                     ContentParent* aOpenerContentParent,
-                     bool aFreshProcess = false);
+  CreateBrowser(const TabContext& aContext,
+                Element* aFrameElement,
+                ContentParent* aOpenerContentParent,
+                bool aFreshProcess = false);
 
   static void GetAll(nsTArray<ContentParent*>& aArray);
 
@@ -231,7 +231,6 @@ public:
                                       const hal::ProcessPriority& aPriority,
                                       const TabId& aOpenerTabId,
                                       ContentParentId* aCpId,
-                                      bool* aIsForApp,
                                       bool* aIsForBrowser,
                                       TabId* aTabId) override;
 
@@ -322,8 +321,6 @@ public:
 
   bool IsAlive() const;
 
-  virtual bool IsForApp() const override;
-
   virtual bool IsForBrowser() const override
   {
     return mIsForBrowser;
@@ -356,8 +353,6 @@ public:
 
   ContentParentId ChildID() const override { return mChildID; }
 
-  const nsString& AppManifestURL() const { return mAppManifestURL; }
-
   bool IsPreallocated() const;
 
   /**
@@ -545,8 +540,7 @@ protected:
   void OnCompositorUnexpectedShutdown() override;
 
 private:
-  static nsDataHashtable<nsStringHashKey, ContentParent*> *sAppContentParents;
-  static nsTArray<ContentParent*>* sNonAppContentParents;
+  static nsTArray<ContentParent*>* sBrowserContentParents;
   static nsTArray<ContentParent*>* sLargeAllocationContentParents;
   static nsTArray<ContentParent*>* sPrivateContent;
   static StaticAutoPtr<LinkedList<ContentParent> > sContentParents;
@@ -554,15 +548,6 @@ private:
   static void JoinProcessesIOThread(const nsTArray<ContentParent*>* aProcesses,
                                     Monitor* aMonitor, bool* aDone);
 
-  // Take the preallocated process and transform it into a "real" app process,
-  // for the specified manifest URL.  If there is no preallocated process (or
-  // if it's dead), create a new one and set aTookPreAllocated to false.
-  static already_AddRefed<ContentParent>
-  GetNewOrPreallocatedAppProcess(mozIApplication* aApp,
-                                 hal::ProcessPriority aInitialPriority,
-                                 ContentParent* aOpener,
-                                 /*out*/ bool* aTookPreAllocated = nullptr);
-
   static hal::ProcessPriority GetInitialProcessPriority(Element* aFrameElement);
 
   static ContentBridgeParent* CreateContentBridgeParent(const TabContext& aContext,
@@ -578,16 +563,14 @@ private:
       const IPCTabContext& context,
       const uint32_t& chromeFlags,
       const ContentParentId& aCpId,
-      const bool& aIsForApp,
       const bool& aIsForBrowser) override;
   using PContentParent::SendPTestShellConstructor;
 
   FORWARD_SHMEM_ALLOCATOR_TO(PContentParent)
 
-  // No more than one of !!aApp, aIsForBrowser, and aIsForPreallocated may be
+  // No more than one of aIsForBrowser, and aIsForPreallocated may be
   // true.
-  ContentParent(mozIApplication* aApp,
-                ContentParent* aOpener,
+  ContentParent(ContentParent* aOpener,
                 bool aIsForBrowser,
                 bool aIsForPreallocated);
 
@@ -609,7 +592,7 @@ private:
 
   // Some information could be sent to content very early, it
   // should be send from this function. This function should only be
-  // called after the process has been transformed to app or browser.
+  // called after the process has been transformed to browser.
   void ForwardKnownInfo();
 
   // Set the child process's priority and then check whether the child is
@@ -618,11 +601,6 @@ private:
   // unlikely that the process will be killed after this point.
   bool SetPriorityAndCheckIsAlive(hal::ProcessPriority aPriority);
 
-  // Transform a pre-allocated app process into a "real" app
-  // process, for the specified manifest URL.
-  void TransformPreallocatedIntoApp(ContentParent* aOpener,
-                                    const nsAString& aAppManifestURL);
-
   // Transform a pre-allocated app process into a browser process. If this
   // returns false, the child process has died.
   void TransformPreallocatedIntoBrowser(ContentParent* aOpener);
@@ -687,7 +665,6 @@ private:
                                  ProcessId aOtherProcess) override;
 
   virtual bool RecvGetProcessAttributes(ContentParentId* aCpId,
-                                        bool* aIsForApp,
                                         bool* aIsForBrowser) override;
 
   virtual bool
@@ -712,7 +689,6 @@ private:
                                               const IPCTabContext& aContext,
                                               const uint32_t& aChromeFlags,
                                               const ContentParentId& aCpId,
-                                              const bool& aIsForApp,
                                               const bool& aIsForBrowser) override;
 
   virtual bool DeallocPBrowserParent(PBrowserParent* frame) override;
@@ -1048,17 +1024,8 @@ private:
   ContentParentId mChildID;
   int32_t mGeolocationWatchID;
 
-  nsString mAppManifestURL;
-
   nsCString mKillHardAnnotation;
 
-  /**
-   * We cache mAppName instead of looking it up using mAppManifestURL when we
-   * need it because it turns out that getting an app from the apps service is
-   * expensive.
-   */
-  nsString mAppName;
-
   // After we initiate shutdown, we also start a timer to ensure
   // that even content processes that are 100% blocked (say from
   // SIGSTOP), are still killed eventually.  This task enforces that
@@ -1074,12 +1041,13 @@ private:
   // through.
   bool mIsAlive;
 
-  // True only the if process is already a browser or app or has
+  // True only the if process is already a browser or has
   // been transformed into one.
   bool mMetamorphosed;
 
   bool mSendPermissionUpdates;
   bool mIsForBrowser;
+  bool mIsPreallocated;
 
   // These variables track whether we've called Close() and KillHard() on our
   // channel.
diff --git a/dom/ipc/ContentProcessManager.cpp b/dom/ipc/ContentProcessManager.cpp
index 9dbb6a7a2c..959daa484c 100644
--- a/dom/ipc/ContentProcessManager.cpp
+++ b/dom/ipc/ContentProcessManager.cpp
@@ -353,19 +353,5 @@ ContentProcessManager::GetTabParentsByProcessId(const ContentParentId& aChildCpI
   return Move(tabIdList);
 }
 
-uint32_t
-ContentProcessManager::GetAppIdByProcessAndTabId(const ContentParentId& aChildCpId,
-                                                 const TabId& aChildTabId)
-{
-  uint32_t appId = nsIScriptSecurityManager::NO_APP_ID;
-  if (aChildCpId && aChildTabId) {
-    TabContext tabContext;
-    if (GetTabContextByProcessAndTabId(aChildCpId, aChildTabId, &tabContext)) {
-      appId = tabContext.OwnOrContainingAppId();
-    }
-  }
-  return appId;
-}
-
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/ipc/ContentProcessManager.h b/dom/ipc/ContentProcessManager.h
index 8e3bb6d3f8..e48e6e2d65 100644
--- a/dom/ipc/ContentProcessManager.h
+++ b/dom/ipc/ContentProcessManager.h
@@ -142,15 +142,6 @@ public:
   GetTopLevelTabParentByProcessAndTabId(const ContentParentId& aChildCpId,
                                         const TabId& aChildTabId);
 
-  /**
-   * Return appId by given TabId and ContentParentId.
-   * It will return nsIScriptSecurityManager::NO_APP_ID
-   * if the given tab is not an app.
-   */
-  uint32_t
-  GetAppIdByProcessAndTabId(const ContentParentId& aChildCpId,
-                            const TabId& aChildTabId);
-
 private:
   static StaticAutoPtr<ContentProcessManager> sSingleton;
   TabId mUniqueId;
diff --git a/dom/ipc/PContent.ipdl b/dom/ipc/PContent.ipdl
index 0bd4f97085..9c45e748ed 100644
--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -272,27 +272,20 @@ both:
     // The child creates the PBrowser as part of
     // TabChild::BrowserFrameProvideWindow (which happens when the child's
     // content calls window.open()), and the parent creates the PBrowser as part
-    // of ContentParent::CreateBrowserOrApp.
+    // of ContentParent::CreateBrowser.
     //
-    // When the parent constructs a PBrowser, the child trusts the app token and
-    // other attributes it receives from the parent.  In that case, the
-    // context should be FrameIPCTabContext.
+    // When the parent constructs a PBrowser, the child trusts the attributes it
+    // receives from the parent.  In that case, the context should be
+    // FrameIPCTabContext.
     //
-    // When the child constructs a PBrowser, the parent doesn't trust the app
-    // token it receives from the child.  In this case, context must have type
-    // PopupIPCTabContext.  The browser created using a PopupIPCTabContext has
-    // the opener PBrowser's app-id and containing-app-id.  The parent checks
-    // that if the opener is a browser element, the context is also for a
-    // browser element.
-    //
-    // This allows the parent to prevent a malicious child from escalating its
-    // privileges by requesting a PBrowser corresponding to a highly-privileged
-    // app; the child can only request privileges for an app which the child has
-    // access to (in the form of a TabChild).
+    // When the child constructs a PBrowser, the parent doesn't trust the
+    // attributes it receives from the child.  In this case, context must have
+    // type PopupIPCTabContext.  The parent checks that if the opener is a
+    // browser element, the context is also for a browser element.
     //
     // Keep the last 3 attributes in sync with GetProcessAttributes!
     async PBrowser(TabId tabId, IPCTabContext context, uint32_t chromeFlags,
-                   ContentParentId cpId, bool isForApp, bool isForBrowser);
+                   ContentParentId cpId, bool isForBrowser);
 
     async PBlob(BlobConstructorParams params);
 
@@ -535,15 +528,13 @@ parent:
      * startup.  (The message is sync to allow the content process to
      * control when it receives the information.)
      *
-     * |id| is a unique ID among all subprocesses.  When |isForApp &&
-     * isForBrowser|, we're loading <browser> for an app.  When
-     * |isForBrowser|, we're loading <browser>.  When |!isForApp &&
-     * !isForBrowser|, we're probably loading <xul:browser remote>.
+     * |id| is a unique ID among all subprocesses. When
+     * |isForBrowser|, we're loading <browser> or <xul:browser remote>.
      *
      * Keep the return values in sync with PBrowser()!
      */
     sync GetProcessAttributes()
-        returns (ContentParentId cpId, bool isForApp, bool isForBrowser);
+        returns (ContentParentId cpId, bool isForBrowser);
     sync GetXPCOMProcessAttributes()
         returns (bool isOffline, bool isConnected, int32_t captivePortalState,
                  bool isLangRTL,
@@ -556,7 +547,7 @@ parent:
     sync CreateChildProcess(IPCTabContext context,
                             ProcessPriority priority,
                             TabId openerTabId)
-        returns (ContentParentId cpId, bool isForApp, bool isForBrowser, TabId tabId);
+        returns (ContentParentId cpId, bool isForBrowser, TabId tabId);
     sync BridgeToChildProcess(ContentParentId cpId);
 
 #ifdef MOZ_GMP
diff --git a/dom/ipc/PContentBridge.ipdl b/dom/ipc/PContentBridge.ipdl
index 6be88653d6..72bf4f3adf 100644
--- a/dom/ipc/PContentBridge.ipdl
+++ b/dom/ipc/PContentBridge.ipdl
@@ -54,7 +54,7 @@ both:
     // Both the parent and the child can construct the PBrowser.
     // See the comment in PContent::PBrowser().
     async PBrowser(TabId tabId, IPCTabContext context, uint32_t chromeFlags,
-                   ContentParentId cpId, bool isForApp, bool isForBrowser);
+                   ContentParentId cpId, bool isForBrowser);
 
     async PBlob(BlobConstructorParams params);
 
diff --git a/dom/ipc/PTabContext.ipdlh b/dom/ipc/PTabContext.ipdlh
index 62d6ec0f35..c201b25fe0 100644
--- a/dom/ipc/PTabContext.ipdlh
+++ b/dom/ipc/PTabContext.ipdlh
@@ -38,9 +38,6 @@ struct FrameIPCTabContext
   // The originAttributes dictionary.
   DocShellOriginAttributes originAttributes;
 
-  // The ID of the app containing this app/browser frame, if applicable.
-  uint32_t frameOwnerAppId;
-
   // Whether this is a mozbrowser frame.  <iframe mozbrowser mozapp> and
   // <xul:browser> are not considered to be mozbrowser frames.
   bool isMozBrowserElement;
diff --git a/dom/ipc/ProcessPriorityManager.cpp b/dom/ipc/ProcessPriorityManager.cpp
index 51c42f7a52..4470a7b156 100644
--- a/dom/ipc/ProcessPriorityManager.cpp
+++ b/dom/ipc/ProcessPriorityManager.cpp
@@ -860,10 +860,10 @@ ParticularProcessPriorityManager::OnRemoteBrowserFrameShown(nsISupports* aSubjec
     return;
   }
 
-  // Ignore notifications that aren't from a BrowserOrApp
-  bool isMozBrowserOrApp;
-  fl->GetOwnerIsMozBrowserOrAppFrame(&isMozBrowserOrApp);
-  if (isMozBrowserOrApp) {
+  // Ignore notifications that aren't from a Browser
+  bool isMozBrowser;
+  fl->GetOwnerIsMozBrowserFrame(&isMozBrowser);
+  if (isMozBrowser) {
     ResetPriority();
   }
 
diff --git a/dom/ipc/TabChild.cpp b/dom/ipc/TabChild.cpp
index caae91fa54..cb853dcb94 100644
--- a/dom/ipc/TabChild.cpp
+++ b/dom/ipc/TabChild.cpp
@@ -410,7 +410,7 @@ TabChild::Create(nsIContentChild* aManager,
 {
     if (sPreallocatedTab &&
         sPreallocatedTab->mChromeFlags == aChromeFlags &&
-        aContext.IsMozBrowserOrApp()) {
+        aContext.IsMozBrowser()) {
 
         RefPtr<TabChild> child = sPreallocatedTab.get();
         sPreallocatedTab = nullptr;
@@ -779,9 +779,9 @@ TabChild::UpdateFrameType()
   MOZ_ASSERT(docShell);
 
   // TODO: Bug 1252794 - remove frameType from nsIDocShell.idl
-  docShell->SetFrameType(IsMozBrowserElement() ? nsIDocShell::FRAME_TYPE_BROWSER :
-                           HasOwnApp() ? nsIDocShell::FRAME_TYPE_APP :
-                             nsIDocShell::FRAME_TYPE_REGULAR);
+  docShell->SetFrameType(IsMozBrowserElement() ?
+                           nsIDocShell::FRAME_TYPE_BROWSER :
+                           nsIDocShell::FRAME_TYPE_REGULAR);
 }
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(TabChild)
@@ -1091,11 +1091,11 @@ TabChild::ProvideWindow(mozIDOMWindowProxy* aParent,
 {
     *aReturn = nullptr;
 
-    // If aParent is inside an <iframe mozbrowser> or <iframe mozapp> and this
-    // isn't a request to open a modal-type window, we're going to create a new
-    // <iframe mozbrowser/mozapp> and return its window here.
+    // If aParent is inside an <iframe mozbrowser> and this isn't a request to
+    // open a modal-type window, we're going to create a new <iframe mozbrowser>
+    // and return its window here.
     nsCOMPtr<nsIDocShell> docshell = do_GetInterface(aParent);
-    bool iframeMoz = (docshell && docshell->GetIsInMozBrowserOrApp() &&
+    bool iframeMoz = (docshell && docshell->GetIsInMozBrowser() &&
                       !(aChromeFlags & (nsIWebBrowserChrome::CHROME_MODAL |
                                         nsIWebBrowserChrome::CHROME_OPENAS_DIALOG |
                                         nsIWebBrowserChrome::CHROME_OPENAS_CHROME)));
@@ -1208,24 +1208,6 @@ TabChild::~TabChild()
   }
 }
 
-void
-TabChild::SetProcessNameToAppName()
-{
-  nsCOMPtr<mozIApplication> app = GetOwnApp();
-  if (!app) {
-    return;
-  }
-
-  nsAutoString appName;
-  nsresult rv = app->GetName(appName);
-  if (NS_FAILED(rv)) {
-    NS_WARNING("Failed to retrieve app name");
-    return;
-  }
-
-  ContentChild::GetSingleton()->SetProcessName(appName, true);
-}
-
 bool
 TabChild::RecvLoadURL(const nsCString& aURI,
                       const ShowInfo& aInfo)
@@ -1237,8 +1219,6 @@ TabChild::RecvLoadURL(const nsCString& aURI,
     }
 
     ApplyShowInfo(aInfo);
-
-    SetProcessNameToAppName();
   }
 
   nsresult rv =
@@ -1279,7 +1259,7 @@ TabChild::ApplyShowInfo(const ShowInfo& aInfo)
   nsCOMPtr<nsIDocShell> docShell = do_GetInterface(WebNavigation());
   if (docShell) {
     nsCOMPtr<nsIDocShellTreeItem> item = do_GetInterface(docShell);
-    if (IsMozBrowserOrApp()) {
+    if (IsMozBrowser()) {
       // B2G allows window.name to be set by changing the name attribute on the
       // <iframe mozbrowser> element. window.open calls cause this attribute to
       // be set to the correct value. A normal <xul:browser> element has no such
@@ -2135,7 +2115,7 @@ TabChild::RecvSwappedWithOtherRemoteLoader(const IPCTabContext& aContext)
   // Ignore previous value of mTriedBrowserInit since owner content has changed.
   mTriedBrowserInit = true;
   // Initialize the child side of the browser element machinery, if appropriate.
-  if (IsMozBrowserOrApp()) {
+  if (IsMozBrowser()) {
     RecvLoadRemoteScript(BROWSER_ELEMENT_CHILD_SCRIPT, true);
   }
 
@@ -2494,7 +2474,7 @@ TabChild::InitTabChildGlobal(FrameScriptLoading aScriptLoading)
     mTriedBrowserInit = true;
     // Initialize the child side of the browser element machinery,
     // if appropriate.
-    if (IsMozBrowserOrApp()) {
+    if (IsMozBrowser()) {
       RecvLoadRemoteScript(BROWSER_ELEMENT_CHILD_SCRIPT, true);
     }
   }
diff --git a/dom/ipc/TabChild.h b/dom/ipc/TabChild.h
index a812b8213a..6282ac48a9 100644
--- a/dom/ipc/TabChild.h
+++ b/dom/ipc/TabChild.h
@@ -707,8 +707,6 @@ private:
 
   void DestroyWindow();
 
-  void SetProcessNameToAppName();
-
   void ApplyShowInfo(const ShowInfo& aInfo);
 
   bool HasValidInnerSize();
diff --git a/dom/ipc/TabContext.cpp b/dom/ipc/TabContext.cpp
index b313da0ffa..fd434fe0cb 100644
--- a/dom/ipc/TabContext.cpp
+++ b/dom/ipc/TabContext.cpp
@@ -7,7 +7,6 @@
 #include "mozilla/dom/PTabContext.h"
 #include "mozilla/dom/TabParent.h"
 #include "mozilla/dom/TabChild.h"
-#include "nsIAppsService.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsServiceManagerUtils.h"
 
@@ -23,7 +22,7 @@ TabContext::TabContext()
   : mIsPrerendered(false)
   , mInitialized(false)
   , mIsMozBrowserElement(false)
-  , mContainingAppId(NO_APP_ID)
+  , mOriginAttributes()
   , mShowAccelerators(UIStateChangeType_NoChange)
   , mShowFocusRings(UIStateChangeType_NoChange)
 {
@@ -36,117 +35,9 @@ TabContext::IsMozBrowserElement() const
 }
 
 bool
-TabContext::IsIsolatedMozBrowserElement() const
+TabContext::IsMozBrowser() const
 {
-  return mOriginAttributes.mInIsolatedMozBrowser;
-}
-
-bool
-TabContext::IsMozBrowserOrApp() const
-{
-  return HasOwnApp() || IsMozBrowserElement();
-}
-
-uint32_t
-TabContext::OwnAppId() const
-{
-  return mOriginAttributes.mAppId;
-}
-
-already_AddRefed<mozIApplication>
-TabContext::GetOwnApp() const
-{
-  nsCOMPtr<mozIApplication> ownApp = mOwnApp;
-  return ownApp.forget();
-}
-
-bool
-TabContext::HasOwnApp() const
-{
-  nsCOMPtr<mozIApplication> ownApp = GetOwnApp();
-  return !!ownApp;
-}
-
-uint32_t
-TabContext::BrowserOwnerAppId() const
-{
-  if (IsMozBrowserElement()) {
-    return mContainingAppId;
-  }
-  return NO_APP_ID;
-}
-
-already_AddRefed<mozIApplication>
-TabContext::GetBrowserOwnerApp() const
-{
-  nsCOMPtr<mozIApplication> ownerApp;
-  if (IsMozBrowserElement()) {
-    ownerApp = mContainingApp;
-  }
-  return ownerApp.forget();
-}
-
-bool
-TabContext::HasBrowserOwnerApp() const
-{
-  nsCOMPtr<mozIApplication> ownerApp = GetBrowserOwnerApp();
-  return !!ownerApp;
-}
-
-uint32_t
-TabContext::AppOwnerAppId() const
-{
-  if (HasOwnApp()) {
-    return mContainingAppId;
-  }
-  return NO_APP_ID;
-}
-
-already_AddRefed<mozIApplication>
-TabContext::GetAppOwnerApp() const
-{
-  nsCOMPtr<mozIApplication> ownerApp;
-  if (HasOwnApp()) {
-    ownerApp = mContainingApp;
-  }
-  return ownerApp.forget();
-}
-
-bool
-TabContext::HasAppOwnerApp() const
-{
-  nsCOMPtr<mozIApplication> ownerApp = GetAppOwnerApp();
-  return !!ownerApp;
-}
-
-uint32_t
-TabContext::OwnOrContainingAppId() const
-{
-  if (HasOwnApp()) {
-    return mOriginAttributes.mAppId;
-  }
-
-  return mContainingAppId;
-}
-
-already_AddRefed<mozIApplication>
-TabContext::GetOwnOrContainingApp() const
-{
-  nsCOMPtr<mozIApplication> ownOrContainingApp;
-  if (HasOwnApp()) {
-    ownOrContainingApp = mOwnApp;
-  } else {
-    ownOrContainingApp = mContainingApp;
-  }
-
-  return ownOrContainingApp.forget();
-}
-
-bool
-TabContext::HasOwnOrContainingApp() const
-{
-  nsCOMPtr<mozIApplication> ownOrContainingApp = GetOwnOrContainingApp();
-  return !!ownOrContainingApp;
+  return IsMozBrowserElement();
 }
 
 bool
@@ -174,9 +65,7 @@ TabContext::UpdateTabContextAfterSwap(const TabContext& aContext)
 
   // The only permissable change is to `mIsMozBrowserElement`.  All other fields
   // must match for the change to be accepted.
-  if (aContext.OwnAppId() != OwnAppId() ||
-      aContext.mContainingAppId != mContainingAppId ||
-      aContext.mOriginAttributes != mOriginAttributes) {
+  if (aContext.mOriginAttributes != mOriginAttributes) {
     return false;
   }
 
@@ -205,42 +94,19 @@ TabContext::ShowFocusRings() const
 bool
 TabContext::SetTabContext(bool aIsMozBrowserElement,
                           bool aIsPrerendered,
-                          mozIApplication* aOwnApp,
-                          mozIApplication* aAppFrameOwnerApp,
                           UIStateChangeType aShowAccelerators,
                           UIStateChangeType aShowFocusRings,
                           const DocShellOriginAttributes& aOriginAttributes)
 {
   NS_ENSURE_FALSE(mInitialized, false);
 
-  // Get ids for both apps and only write to our member variables after we've
-  // verified that this worked.
-  uint32_t ownAppId = NO_APP_ID;
-  if (aOwnApp) {
-    nsresult rv = aOwnApp->GetLocalId(&ownAppId);
-    NS_ENSURE_SUCCESS(rv, false);
-    NS_ENSURE_TRUE(ownAppId != NO_APP_ID, false);
-  }
-
-  uint32_t containingAppId = NO_APP_ID;
-  if (aAppFrameOwnerApp) {
-    nsresult rv = aAppFrameOwnerApp->GetLocalId(&containingAppId);
-    NS_ENSURE_SUCCESS(rv, false);
-    NS_ENSURE_TRUE(containingAppId != NO_APP_ID, false);
-  }
-
-  // Veryify that app id matches mAppId passed in originAttributes
-  MOZ_RELEASE_ASSERT((aOwnApp && aOriginAttributes.mAppId == ownAppId) ||
-                     (aAppFrameOwnerApp && aOriginAttributes.mAppId == containingAppId) ||
-                     aOriginAttributes.mAppId == NO_APP_ID);
+  // Verify that app id matches mAppId passed in originAttributes
+  MOZ_RELEASE_ASSERT(aOriginAttributes.mAppId == NO_APP_ID);
 
   mInitialized = true;
   mIsMozBrowserElement = aIsMozBrowserElement;
   mIsPrerendered = aIsPrerendered;
   mOriginAttributes = aOriginAttributes;
-  mContainingAppId = containingAppId;
-  mOwnApp = aOwnApp;
-  mContainingApp = aAppFrameOwnerApp;
   mShowAccelerators = aShowAccelerators;
   mShowFocusRings = aShowFocusRings;
   return true;
@@ -250,31 +116,17 @@ IPCTabContext
 TabContext::AsIPCTabContext() const
 {
   return IPCTabContext(FrameIPCTabContext(mOriginAttributes,
-                                          mContainingAppId,
                                           mIsMozBrowserElement,
                                           mIsPrerendered,
                                           mShowAccelerators,
                                           mShowFocusRings));
 }
 
-static already_AddRefed<mozIApplication>
-GetAppForId(uint32_t aAppId)
-{
-  nsCOMPtr<nsIAppsService> appsService = do_GetService(APPS_SERVICE_CONTRACTID);
-  NS_ENSURE_TRUE(appsService, nullptr);
-
-  nsCOMPtr<mozIApplication> app;
-  appsService->GetAppByLocalId(aAppId, getter_AddRefs(app));
-
-  return app.forget();
-}
-
 MaybeInvalidTabContext::MaybeInvalidTabContext(const IPCTabContext& aParams)
   : mInvalidReason(nullptr)
 {
   bool isMozBrowserElement = false;
   bool isPrerendered = false;
-  uint32_t containingAppId = NO_APP_ID;
   DocShellOriginAttributes originAttributes;
   UIStateChangeType showAccelerators = UIStateChangeType_NoChange;
   UIStateChangeType showFocusRings = UIStateChangeType_NoChange;
@@ -324,11 +176,6 @@ MaybeInvalidTabContext::MaybeInvalidTabContext(const IPCTabContext& aParams)
       // opener app.
       isMozBrowserElement = ipcContext.isMozBrowserElement();
       originAttributes = context->mOriginAttributes;
-      if (isMozBrowserElement) {
-        containingAppId = context->OwnOrContainingAppId();
-      } else {
-        containingAppId = context->mContainingAppId;
-      }
       break;
     }
     case IPCTabContext::TFrameIPCTabContext: {
@@ -337,7 +184,6 @@ MaybeInvalidTabContext::MaybeInvalidTabContext(const IPCTabContext& aParams)
 
       isMozBrowserElement = ipcContext.isMozBrowserElement();
       isPrerendered = ipcContext.isPrerendered();
-      containingAppId = ipcContext.frameOwnerAppId();
       showAccelerators = ipcContext.showAccelerators();
       showFocusRings = ipcContext.showFocusRings();
       originAttributes = ipcContext.originAttributes();
@@ -352,7 +198,6 @@ MaybeInvalidTabContext::MaybeInvalidTabContext(const IPCTabContext& aParams)
         return;
       }
 
-      containingAppId = NO_APP_ID;
       break;
     }
     default: {
@@ -360,28 +205,9 @@ MaybeInvalidTabContext::MaybeInvalidTabContext(const IPCTabContext& aParams)
     }
   }
 
-  nsCOMPtr<mozIApplication> ownApp;
-  if (!isMozBrowserElement) {
-    // mAppId corresponds to OwnOrContainingAppId; if isMozBrowserElement is
-    // false then it's ownApp otherwise it's containingApp
-    ownApp = GetAppForId(originAttributes.mAppId);
-    if ((ownApp == nullptr) != (originAttributes.mAppId == NO_APP_ID)) {
-      mInvalidReason = "Got an ownAppId that didn't correspond to an app.";
-      return;
-    }
-  }
-
-  nsCOMPtr<mozIApplication> containingApp = GetAppForId(containingAppId);
-  if ((containingApp == nullptr) != (containingAppId == NO_APP_ID)) {
-    mInvalidReason = "Got a containingAppId that didn't correspond to an app.";
-    return;
-  }
-
   bool rv;
   rv = mTabContext.SetTabContext(isMozBrowserElement,
                                  isPrerendered,
-                                 ownApp,
-                                 containingApp,
                                  showAccelerators,
                                  showFocusRings,
                                  originAttributes);
diff --git a/dom/ipc/TabContext.h b/dom/ipc/TabContext.h
index e0b6f0d963..8bb21dc1e0 100644
--- a/dom/ipc/TabContext.h
+++ b/dom/ipc/TabContext.h
@@ -6,7 +6,6 @@
 #ifndef mozilla_dom_TabContext_h
 #define mozilla_dom_TabContext_h
 
-#include "mozIApplication.h"
 #include "nsCOMPtr.h"
 #include "mozilla/BasePrincipal.h"
 #include "nsPIDOMWindow.h"
@@ -18,9 +17,7 @@ namespace dom {
 class IPCTabContext;
 
 /**
- * TabContext encapsulates information about an iframe that may be a mozbrowser
- * or mozapp.  You can ask whether a TabContext corresponds to a mozbrowser or
- * mozapp, get the app that contains the browser, and so on.
+ * TabContext encapsulates information about an iframe that may be a mozbrowser.
  *
  * TabParent and TabChild both inherit from TabContext, and you can also have
  * standalone TabContext objects.
@@ -37,91 +34,29 @@ public:
   /* (The implicit copy-constructor and operator= are fine.) */
 
   /**
-   * Generates IPCTabContext of type BrowserFrameIPCTabContext or
-   * AppFrameIPCTabContext from this TabContext's information.
+   * Generates IPCTabContext of type BrowserFrameIPCTabContext from this
+   * TabContext's information.
    */
   IPCTabContext AsIPCTabContext() const;
 
   /**
    * Does this TabContext correspond to a mozbrowser?
    *
-   * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
-   * mozbrowser elements.
-   *
-   * If IsMozBrowserElement() is true, HasOwnApp() and HasAppOwnerApp() are
-   * guaranteed to be false.
-   *
-   * If IsMozBrowserElement() is false, HasBrowserOwnerApp() is guaranteed to be
-   * false.
+   * <iframe mozbrowser> is a mozbrowser element, but <xul:browser> is not.
    */
   bool IsMozBrowserElement() const;
 
   /**
-   * Does this TabContext correspond to an isolated mozbrowser?
-   *
-   * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
-   * mozbrowser elements.  <iframe mozbrowser noisolation> does not count as
-   * isolated since isolation is disabled.  Isolation can only be disabled by
-   * chrome pages.
+   * Does this TabContext correspond to a mozbrowser?  This is equivalent to
+   * IsMozBrowserElement().  Returns false for <xul:browser>, which isn't a
+   * mozbrowser.
    */
-  bool IsIsolatedMozBrowserElement() const;
-
-  /**
-   * Does this TabContext correspond to a mozbrowser or mozapp?  This is
-   * equivalent to IsMozBrowserElement() || HasOwnApp().  Returns false for
-   * <xul:browser>, which is neither a mozbrowser nor a mozapp.
-   */
-  bool IsMozBrowserOrApp() const;
-
-  /**
-   * OwnAppId() returns the id of the app which directly corresponds to this
-   * context's frame.  GetOwnApp() returns the corresponding app object, and
-   * HasOwnApp() returns true iff GetOwnApp() would return a non-null value.
-   *
-   * If HasOwnApp() is true, IsMozBrowserElement() is guaranteed to be
-   * false.
-   */
-  uint32_t OwnAppId() const;
-  already_AddRefed<mozIApplication> GetOwnApp() const;
-  bool HasOwnApp() const;
-
-  /**
-   * BrowserOwnerAppId() gets the ID of the app which contains this browser
-   * frame.  If this is not a mozbrowser frame (if !IsMozBrowserElement()), then
-   * BrowserOwnerAppId() is guaranteed to return NO_APP_ID.
-   *
-   * Even if we are a browser frame, BrowserOwnerAppId() may still return
-   * NO_APP_ID, if this browser frame is not contained inside an app.
-   */
-  uint32_t BrowserOwnerAppId() const;
-  already_AddRefed<mozIApplication> GetBrowserOwnerApp() const;
-  bool HasBrowserOwnerApp() const;
-
-  /**
-   * AppOwnerAppId() gets the ID of the app which contains this app frame.  If
-   * this is not an app frame (i.e., if !HasOwnApp()), then AppOwnerAppId() is
-   * guaranteed to return NO_APP_ID.
-   *
-   * Even if we are an app frame, AppOwnerAppId() may still return NO_APP_ID, if
-   * this app frame is not contained inside an app.
-   */
-  uint32_t AppOwnerAppId() const;
-  already_AddRefed<mozIApplication> GetAppOwnerApp() const;
-  bool HasAppOwnerApp() const;
-
-  /**
-   * OwnOrContainingAppId() gets the ID of this frame, if HasOwnApp().  If this
-   * frame does not have its own app, it gets the ID of the app which contains
-   * this frame (i.e., the result of {Browser,App}OwnerAppId(), as applicable).
-   */
-  uint32_t OwnOrContainingAppId() const;
-  already_AddRefed<mozIApplication> GetOwnOrContainingApp() const;
-  bool HasOwnOrContainingApp() const;
+  bool IsMozBrowser() const;
 
   /**
    * OriginAttributesRef() returns the DocShellOriginAttributes of this frame to
    * the caller. This is used to store any attribute associated with the frame's
-   * docshell, such as the AppId.
+   * docshell.
    */
   const DocShellOriginAttributes& OriginAttributesRef() const;
 
@@ -150,17 +85,8 @@ protected:
    */
   void SetPrivateBrowsingAttributes(bool aIsPrivateBrowsing);
 
-  /**
-   * Set the TabContext for this frame. This can either be:
-   *  - an app frame (with the given own app) inside the given owner app. Either
-   *    apps can be null.
-   *  - a browser frame inside the given owner app (which may be null).
-   *  - a non-browser, non-app frame. Both own app and owner app should be null.
-   */
   bool SetTabContext(bool aIsMozBrowserElement,
                      bool aIsPrerendered,
-                     mozIApplication* aOwnApp,
-                     mozIApplication* aAppFrameOwnerApp,
                      UIStateChangeType aShowAccelerators,
                      UIStateChangeType aShowFocusRings,
                      const DocShellOriginAttributes& aOriginAttributes);
@@ -190,29 +116,11 @@ private:
   /**
    * Whether this TabContext corresponds to a mozbrowser.
    *
-   * <iframe mozbrowser mozapp> and <xul:browser> are not considered to be
+   * <iframe mozbrowser> and <xul:browser> are not considered to be
    * mozbrowser elements.
    */
   bool mIsMozBrowserElement;
 
-  /**
-   * This TabContext's own app.  If this is non-null, then this
-   * TabContext corresponds to an app, and mIsMozBrowserElement must be false.
-   */
-  nsCOMPtr<mozIApplication> mOwnApp;
-
-  /**
-   * This TabContext's containing app.  If mIsMozBrowserElement, this
-   * corresponds to the app which contains the browser frame; otherwise, this
-   * corresponds to the app which contains the app frame.
-   */
-  nsCOMPtr<mozIApplication> mContainingApp;
-
-  /*
-   * Cache of mContainingApp->GetLocalId().
-   */
-  uint32_t mContainingAppId;
-
   /**
    * DocShellOriginAttributes of the top level tab docShell
    */
@@ -241,16 +149,12 @@ public:
   bool
   SetTabContext(bool aIsMozBrowserElement,
                 bool aIsPrerendered,
-                mozIApplication* aOwnApp,
-                mozIApplication* aAppFrameOwnerApp,
                 UIStateChangeType aShowAccelerators,
                 UIStateChangeType aShowFocusRings,
                 const DocShellOriginAttributes& aOriginAttributes)
   {
     return TabContext::SetTabContext(aIsMozBrowserElement,
                                      aIsPrerendered,
-                                     aOwnApp,
-                                     aAppFrameOwnerApp,
                                      aShowAccelerators,
                                      aShowFocusRings,
                                      aOriginAttributes);
@@ -261,10 +165,9 @@ public:
  * MaybeInvalidTabContext is a simple class that lets you transform an
  * IPCTabContext into a TabContext.
  *
- * The issue is that an IPCTabContext is not necessarily valid; for example, it
- * might specify an app-id which doesn't exist.  So to convert an IPCTabContext
- * into a TabContext, you construct a MaybeInvalidTabContext, check whether it's
- * valid, and, if so, read out your TabContext.
+ * The issue is that an IPCTabContext is not necessarily valid.  So to convert
+ * an IPCTabContext into a TabContext, you construct a MaybeInvalidTabContext,
+ * check whether it's valid, and, if so, read out your TabContext.
  *
  * Example usage:
  *
diff --git a/dom/ipc/TabParent.cpp b/dom/ipc/TabParent.cpp
index a3d2556ae1..3c58dbecc3 100644
--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -9,7 +9,6 @@
 
 #include "AudioChannelService.h"
 #include "AppProcessChecker.h"
-#include "mozIApplication.h"
 #ifdef ACCESSIBILITY
 #include "mozilla/a11y/DocAccessibleParent.h"
 #include "nsAccessibilityService.h"
@@ -2940,8 +2939,6 @@ public:
   NS_IMETHOD GetUsePrivateBrowsing(bool*) NO_IMPL
   NS_IMETHOD SetUsePrivateBrowsing(bool) NO_IMPL
   NS_IMETHOD SetPrivateBrowsing(bool) NO_IMPL
-  NS_IMETHOD GetIsInIsolatedMozBrowserElement(bool*) NO_IMPL
-  NS_IMETHOD GetAppId(uint32_t*) NO_IMPL
   NS_IMETHOD GetOriginAttributes(JS::MutableHandleValue) NO_IMPL
   NS_IMETHOD GetUseRemoteTabs(bool*) NO_IMPL
   NS_IMETHOD SetRemoteTabs(bool) NO_IMPL
diff --git a/dom/ipc/nsIContentChild.cpp b/dom/ipc/nsIContentChild.cpp
index f604dc1a58..84727a8051 100644
--- a/dom/ipc/nsIContentChild.cpp
+++ b/dom/ipc/nsIContentChild.cpp
@@ -43,7 +43,6 @@ nsIContentChild::AllocPBrowserChild(const TabId& aTabId,
                                     const IPCTabContext& aContext,
                                     const uint32_t& aChromeFlags,
                                     const ContentParentId& aCpID,
-                                    const bool& aIsForApp,
                                     const bool& aIsForBrowser)
 {
   // We'll happily accept any kind of IPCTabContext here; we don't need to
diff --git a/dom/ipc/nsIContentChild.h b/dom/ipc/nsIContentChild.h
index 59dffe6b69..2b563a81e5 100644
--- a/dom/ipc/nsIContentChild.h
+++ b/dom/ipc/nsIContentChild.h
@@ -68,7 +68,6 @@ public:
                           const IPCTabContext& aContext,
                           const uint32_t& aChromeFlags,
                           const ContentParentId& aCpID,
-                          const bool& aIsForApp,
                           const bool& aIsForBrowser) = 0;
 
   virtual mozilla::ipc::PFileDescriptorSetChild*
@@ -85,7 +84,6 @@ protected:
                                             const IPCTabContext& aContext,
                                             const uint32_t& aChromeFlags,
                                             const ContentParentId& aCpId,
-                                            const bool& aIsForApp,
                                             const bool& aIsForBrowser);
   virtual bool DeallocPBrowserChild(PBrowserChild*);
 
diff --git a/dom/ipc/nsIContentParent.cpp b/dom/ipc/nsIContentParent.cpp
index 2ff4fcdfc8..fdb6734e9c 100644
--- a/dom/ipc/nsIContentParent.cpp
+++ b/dom/ipc/nsIContentParent.cpp
@@ -122,11 +122,9 @@ nsIContentParent::AllocPBrowserParent(const TabId& aTabId,
                                       const IPCTabContext& aContext,
                                       const uint32_t& aChromeFlags,
                                       const ContentParentId& aCpId,
-                                      const bool& aIsForApp,
                                       const bool& aIsForBrowser)
 {
   Unused << aCpId;
-  Unused << aIsForApp;
   Unused << aIsForBrowser;
 
   if (!CanOpenBrowser(aContext)) {
diff --git a/dom/ipc/nsIContentParent.h b/dom/ipc/nsIContentParent.h
index 6fae9060cb..c883e23695 100644
--- a/dom/ipc/nsIContentParent.h
+++ b/dom/ipc/nsIContentParent.h
@@ -60,7 +60,6 @@ public:
   BlobParent* GetOrCreateActorForBlobImpl(BlobImpl* aImpl);
 
   virtual ContentParentId ChildID() const = 0;
-  virtual bool IsForApp() const = 0;
   virtual bool IsForBrowser() const = 0;
 
   MOZ_MUST_USE virtual PBlobParent*
@@ -73,7 +72,6 @@ public:
                           const IPCTabContext& context,
                           const uint32_t& chromeFlags,
                           const ContentParentId& aCpId,
-                          const bool& aIsForApp,
                           const bool& aIsForBrowser) = 0;
 
   virtual bool IsContentParent() const { return false; }
@@ -99,7 +97,6 @@ protected: // IPDL methods
                                               const IPCTabContext& aContext,
                                               const uint32_t& aChromeFlags,
                                               const ContentParentId& aCpId,
-                                              const bool& aIsForApp,
                                               const bool& aIsForBrowser);
   virtual bool DeallocPBrowserParent(PBrowserParent* frame);
 
diff --git a/dom/media/MediaManager.cpp b/dom/media/MediaManager.cpp
index 0270643cbd..970ece733b 100644
--- a/dom/media/MediaManager.cpp
+++ b/dom/media/MediaManager.cpp
@@ -1893,29 +1893,15 @@ MediaManager::NotifyRecordingStatusChange(nsPIDOMWindowInner* aWindow,
   props->SetPropertyAsBool(NS_LITERAL_STRING("isAudio"), aIsAudio);
   props->SetPropertyAsBool(NS_LITERAL_STRING("isVideo"), aIsVideo);
 
-  bool isApp = false;
-  nsString requestURL;
+  nsCString pageURL;
+  nsCOMPtr<nsIURI> docURI = aWindow->GetDocumentURI();
+  NS_ENSURE_TRUE(docURI, NS_ERROR_FAILURE);
 
-  if (nsCOMPtr<nsIDocShell> docShell = aWindow->GetDocShell()) {
-    isApp = docShell->GetIsApp();
-    if (isApp) {
-      nsresult rv = docShell->GetAppManifestURL(requestURL);
-      NS_ENSURE_SUCCESS(rv, rv);
-    }
-  }
+  nsresult rv = docURI->GetSpec(pageURL);
+  NS_ENSURE_SUCCESS(rv, rv);
 
-  if (!isApp) {
-    nsCString pageURL;
-    nsCOMPtr<nsIURI> docURI = aWindow->GetDocumentURI();
-    NS_ENSURE_TRUE(docURI, NS_ERROR_FAILURE);
+  NS_ConvertUTF8toUTF16 requestURL(pageURL);
 
-    nsresult rv = docURI->GetSpec(pageURL);
-    NS_ENSURE_SUCCESS(rv, rv);
-
-    requestURL = NS_ConvertUTF8toUTF16(pageURL);
-  }
-
-  props->SetPropertyAsBool(NS_LITERAL_STRING("isApp"), isApp);
   props->SetPropertyAsAString(NS_LITERAL_STRING("requestURL"), requestURL);
 
   obs->NotifyObservers(static_cast<nsIPropertyBag2*>(props),
diff --git a/dom/network/TCPServerSocketParent.cpp b/dom/network/TCPServerSocketParent.cpp
index 8e05c6088f..91238e0349 100644
--- a/dom/network/TCPServerSocketParent.cpp
+++ b/dom/network/TCPServerSocketParent.cpp
@@ -67,25 +67,13 @@ TCPServerSocketParent::Init()
 uint32_t
 TCPServerSocketParent::GetAppId()
 {
-  const PContentParent *content = Manager()->Manager();
-  if (PBrowserParent* browser = SingleManagedOrNull(content->ManagedPBrowserParent())) {
-    TabParent *tab = TabParent::GetFrom(browser);
-    return tab->OwnAppId();
-  } else {
-    return nsIScriptSecurityManager::UNKNOWN_APP_ID;
-  }
+  return nsIScriptSecurityManager::UNKNOWN_APP_ID;
 }
 
 bool
 TCPServerSocketParent::GetInIsolatedMozBrowser()
 {
-  const PContentParent *content = Manager()->Manager();
-  if (PBrowserParent* browser = SingleManagedOrNull(content->ManagedPBrowserParent())) {
-    TabParent *tab = TabParent::GetFrom(browser);
-    return tab->IsIsolatedMozBrowserElement();
-  } else {
-    return false;
-  }
+  return false;
 }
 
 nsresult
diff --git a/dom/network/TCPSocketParent.cpp b/dom/network/TCPSocketParent.cpp
index 0e7f0e17ae..d8bd95576e 100644
--- a/dom/network/TCPSocketParent.cpp
+++ b/dom/network/TCPSocketParent.cpp
@@ -73,25 +73,13 @@ TCPSocketParentBase::~TCPSocketParentBase()
 uint32_t
 TCPSocketParent::GetAppId()
 {
-  const PContentParent *content = Manager()->Manager();
-  if (PBrowserParent* browser = SingleManagedOrNull(content->ManagedPBrowserParent())) {
-    TabParent *tab = TabParent::GetFrom(browser);
-    return tab->OwnAppId();
-  } else {
-    return nsIScriptSecurityManager::UNKNOWN_APP_ID;
-  }
-};
+  return nsIScriptSecurityManager::UNKNOWN_APP_ID;
+}
 
 bool
 TCPSocketParent::GetInIsolatedMozBrowser()
 {
-  const PContentParent *content = Manager()->Manager();
-  if (PBrowserParent* browser = SingleManagedOrNull(content->ManagedPBrowserParent())) {
-    TabParent *tab = TabParent::GetFrom(browser);
-    return tab->IsIsolatedMozBrowserElement();
-  } else {
-    return false;
-  }
+  return false;
 }
 
 void
@@ -225,20 +213,11 @@ TCPSocketParent::RecvOpenBind(const nsCString& aRemoteHost,
     }
   }
 
-  // Obtain App ID
-  uint32_t appId = nsIScriptSecurityManager::NO_APP_ID;
   bool     inIsolatedMozBrowser = false;
   const PContentParent *content = Manager()->Manager();
-  if (PBrowserParent* browser = SingleManagedOrNull(content->ManagedPBrowserParent())) {
-    // appId's are for B2G only currently, where managees.Count() == 1
-    // This is not guaranteed currently in Desktop, so skip this there.
-    TabParent *tab = TabParent::GetFrom(browser);
-    appId = tab->OwnAppId();
-    inIsolatedMozBrowser = tab->IsIsolatedMozBrowserElement();
-  }
 
   mSocket = new TCPSocket(nullptr, NS_ConvertUTF8toUTF16(aRemoteHost), aRemotePort, aUseSSL, aUseArrayBuffers);
-  mSocket->SetAppIdAndBrowser(appId, inIsolatedMozBrowser);
+  mSocket->SetAppIdAndBrowser(nsIScriptSecurityManager::NO_APP_ID, inIsolatedMozBrowser);
   mSocket->SetSocketBridgeParent(this);
   rv = mSocket->InitWithUnconnectedTransport(socketTransport);
   NS_ENSURE_SUCCESS(rv, true);
diff --git a/dom/webidl/HTMLIFrameElement.webidl b/dom/webidl/HTMLIFrameElement.webidl
index d2859c6dbc..248e9c7fee 100644
--- a/dom/webidl/HTMLIFrameElement.webidl
+++ b/dom/webidl/HTMLIFrameElement.webidl
@@ -63,11 +63,5 @@ partial interface HTMLIFrameElement {
            attribute boolean mozbrowser;
 };
 
-partial interface HTMLIFrameElement {
-  // nsIMozBrowserFrame
-  [ChromeOnly]
-  readonly attribute DOMString appManifestURL;
-};
-
 HTMLIFrameElement implements MozFrameLoaderOwner;
 HTMLIFrameElement implements BrowserElement;
diff --git a/dom/xul/nsXULElement.cpp b/dom/xul/nsXULElement.cpp
index 96e6cc516f..961de20ee3 100644
--- a/dom/xul/nsXULElement.cpp
+++ b/dom/xul/nsXULElement.cpp
@@ -1619,17 +1619,6 @@ nsXULElement::GetFrameLoader()
     return already_AddRefed<nsFrameLoader>(static_cast<nsFrameLoader*>(loader.forget().take()));
 }
 
-nsresult
-nsXULElement::GetParentApplication(mozIApplication** aApplication)
-{
-    if (!aApplication) {
-        return NS_ERROR_FAILURE;
-    }
-
-    *aApplication = nullptr;
-    return NS_OK;
-}
-
 void
 nsXULElement::PresetOpenerWindow(mozIDOMWindowProxy* aWindow, ErrorResult& aRv)
 {
diff --git a/dom/xul/nsXULElement.h b/dom/xul/nsXULElement.h
index a307141452..87e0dd3144 100644
--- a/dom/xul/nsXULElement.h
+++ b/dom/xul/nsXULElement.h
@@ -412,7 +412,6 @@ public:
     virtual mozilla::EventStates IntrinsicState() const override;
 
     nsresult GetFrameLoaderXPCOM(nsIFrameLoader** aFrameLoader);
-    nsresult GetParentApplication(mozIApplication** aApplication);
     void PresetOpenerWindow(mozIDOMWindowProxy* aWindow, ErrorResult& aRv);
     nsresult SetIsPrerendered();
 
diff --git a/embedding/components/windowwatcher/nsWindowWatcher.cpp b/embedding/components/windowwatcher/nsWindowWatcher.cpp
index 7839228cfc..aa4d5e3914 100644
--- a/embedding/components/windowwatcher/nsWindowWatcher.cpp
+++ b/embedding/components/windowwatcher/nsWindowWatcher.cpp
@@ -1982,7 +1982,7 @@ nsWindowWatcher::CalculateChromeFlagsForParent(mozIDOMWindowProxy* aParent,
   // Disable CHROME_OPENAS_DIALOG if the window is inside <iframe mozbrowser>.
   // It's up to the embedder to interpret what dialog=1 means.
   nsCOMPtr<nsIDocShell> docshell = do_GetInterface(aParent);
-  if (docshell && docshell->GetIsInMozBrowserOrApp()) {
+  if (docshell && docshell->GetIsInMozBrowser()) {
     chromeFlags &= ~nsIWebBrowserChrome::CHROME_OPENAS_DIALOG;
   }
 
diff --git a/extensions/cookie/nsPermissionManager.cpp b/extensions/cookie/nsPermissionManager.cpp
index afdaea63f1..aa2d6d47ac 100644
--- a/extensions/cookie/nsPermissionManager.cpp
+++ b/extensions/cookie/nsPermissionManager.cpp
@@ -30,7 +30,6 @@
 #include "nsContentUtils.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsIAppsService.h"
-#include "mozIApplication.h"
 #include "nsIEffectiveTLDService.h"
 #include "nsPIDOMWindow.h"
 #include "nsIDocument.h"
diff --git a/layout/base/nsPresShell.cpp b/layout/base/nsPresShell.cpp
index 36de447a32..015dbcc078 100644
--- a/layout/base/nsPresShell.cpp
+++ b/layout/base/nsPresShell.cpp
@@ -6882,20 +6882,6 @@ CheckPermissionForBeforeAfterKeyboardEvent(Element* aElement)
     if (permission == nsIPermissionManager::ALLOW_ACTION) {
       return true;
     }
-
-    // Check "embed-apps" permission for later use.
-    permission = nsIPermissionManager::DENY_ACTION;
-    permMgr->TestPermissionFromPrincipal(principal, "embed-apps", &permission);
-  }
-
-  // An element can handle before events and after events if the following
-  // conditions are met:
-  // 1) <iframe mozbrowser mozapp>
-  // 2) it has "embed-apps" permission.
-  nsCOMPtr<nsIMozBrowserFrame> browserFrame(do_QueryInterface(aElement));
-  if ((permission == nsIPermissionManager::ALLOW_ACTION) &&
-      browserFrame && browserFrame->GetReallyIsApp()) {
-    return true;
   }
 
   return false;
diff --git a/layout/generic/nsViewportFrame.cpp b/layout/generic/nsViewportFrame.cpp
index ab3bfc88c3..dac4f22f74 100644
--- a/layout/generic/nsViewportFrame.cpp
+++ b/layout/generic/nsViewportFrame.cpp
@@ -86,7 +86,7 @@ ShouldInTopLayerForFullscreen(Element* aElement)
     return false;
   }
   nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(aElement);
-  if (browserFrame && browserFrame->GetReallyIsBrowserOrApp()) {
+  if (browserFrame && browserFrame->GetReallyIsBrowser()) {
     return false;
   }
   return true;
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index 0a9c55fc17..6abfd57574 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -2310,7 +2310,7 @@ static bool SelectorMatches(Element* aElement,
           nsCOMPtr<nsIMozBrowserFrame>
             browserFrame = do_QueryInterface(aElement);
           if (!browserFrame ||
-              !browserFrame->GetReallyIsBrowserOrApp()) {
+              !browserFrame->GetReallyIsBrowser()) {
             return false;
           }
         }
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 1960cda652..064a6be7ed 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -960,8 +960,6 @@ pref("devtools.debugger.force-local", true);
 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");
 
 // DevTools default color unit
 pref("devtools.defaultColorUnit", "authored");
diff --git a/netwerk/base/nsNetUtil.cpp b/netwerk/base/nsNetUtil.cpp
index b9ec64ef84..b9a07f34a1 100644
--- a/netwerk/base/nsNetUtil.cpp
+++ b/netwerk/base/nsNetUtil.cpp
@@ -568,16 +568,7 @@ NS_LoadGroupMatchesPrincipal(nsILoadGroup *aLoadGroup,
                                   getter_AddRefs(loadContext));
     NS_ENSURE_TRUE(loadContext, false);
 
-    // Verify load context appId and browser flag match the principal
-    uint32_t contextAppId;
-    bool contextInIsolatedBrowser;
-    nsresult rv = loadContext->GetAppId(&contextAppId);
-    NS_ENSURE_SUCCESS(rv, false);
-    rv = loadContext->GetIsInIsolatedMozBrowserElement(&contextInIsolatedBrowser);
-    NS_ENSURE_SUCCESS(rv, false);
-
-    return contextAppId == aPrincipal->GetAppId() &&
-           contextInIsolatedBrowser == aPrincipal->GetIsInIsolatedMozBrowserElement();
+    return true;
 }
 
 nsresult
@@ -2385,39 +2376,18 @@ NS_CompareLoadInfoAndLoadContext(nsIChannel *aChannel)
     return NS_OK;
   }
 
-  uint32_t loadContextAppId = 0;
-  nsresult rv = loadContext->GetAppId(&loadContextAppId);
-  if (NS_FAILED(rv)) {
-    return NS_ERROR_UNEXPECTED;
-  }
-
-  bool loadContextIsInBE = false;
-  rv = loadContext->GetIsInIsolatedMozBrowserElement(&loadContextIsInBE);
-  if (NS_FAILED(rv)) {
-    return NS_ERROR_UNEXPECTED;
-  }
-
   OriginAttributes originAttrsLoadInfo = loadInfo->GetOriginAttributes();
   DocShellOriginAttributes originAttrsLoadContext;
   loadContext->GetOriginAttributes(originAttrsLoadContext);
 
-  LOG(("NS_CompareLoadInfoAndLoadContext - loadInfo: %d, %d, %d, %d; "
-       "loadContext: %d %d, %d, %d. [channel=%p]",
-       originAttrsLoadInfo.mAppId, originAttrsLoadInfo.mInIsolatedMozBrowser,
-       originAttrsLoadInfo.mUserContextId, originAttrsLoadInfo.mPrivateBrowsingId,
-       loadContextAppId, loadContextIsInBE,
-       originAttrsLoadContext.mUserContextId, originAttrsLoadContext.mPrivateBrowsingId,
+  LOG(("NS_CompareLoadInfoAndLoadContext - loadInfo: %d, %d; "
+       "loadContext: %d, %d. [channel=%p]",
+       originAttrsLoadInfo.mUserContextId,
+       originAttrsLoadInfo.mPrivateBrowsingId,
+       originAttrsLoadContext.mUserContextId,
+       originAttrsLoadContext.mPrivateBrowsingId,
        aChannel));
 
-  MOZ_ASSERT(originAttrsLoadInfo.mAppId == loadContextAppId,
-             "AppId in the loadContext and in the loadInfo are not the "
-             "same!");
-
-  MOZ_ASSERT(originAttrsLoadInfo.mInIsolatedMozBrowser ==
-             loadContextIsInBE,
-             "The value of InIsolatedMozBrowser in the loadContext and in "
-             "the loadInfo are not the same!");
-
   MOZ_ASSERT(originAttrsLoadInfo.mUserContextId ==
              originAttrsLoadContext.mUserContextId,
              "The value of mUserContextId in the loadContext and in the "
diff --git a/netwerk/base/nsUDPSocket.cpp b/netwerk/base/nsUDPSocket.cpp
index 3cf45cf328..7aaf6b2654 100644
--- a/netwerk/base/nsUDPSocket.cpp
+++ b/netwerk/base/nsUDPSocket.cpp
@@ -612,8 +612,7 @@ nsUDPSocket::InitWithAddress(const NetAddr *aAddr, nsIPrincipal *aPrincipal,
 
   if (aPrincipal) {
     mAppId = aPrincipal->GetAppId();
-    mIsInIsolatedMozBrowserElement =
-      aPrincipal->GetIsInIsolatedMozBrowserElement();
+    mIsInIsolatedMozBrowserElement = false;
   }
 
   uint16_t port;
diff --git a/netwerk/cookie/nsCookieService.cpp b/netwerk/cookie/nsCookieService.cpp
index bdcb388373..cc996a201a 100644
--- a/netwerk/cookie/nsCookieService.cpp
+++ b/netwerk/cookie/nsCookieService.cpp
@@ -49,7 +49,6 @@
 #include "mozilla/AutoRestore.h"
 #include "mozilla/FileUtils.h"
 #include "nsIAppsService.h"
-#include "mozIApplication.h"
 #include "mozIApplicationClearPrivateDataParams.h"
 #include "nsIConsoleService.h"
 #include "nsVariant.h"
diff --git a/netwerk/protocol/http/HttpBaseChannel.cpp b/netwerk/protocol/http/HttpBaseChannel.cpp
index e0ccbfb811..3c5fa6763a 100644
--- a/netwerk/protocol/http/HttpBaseChannel.cpp
+++ b/netwerk/protocol/http/HttpBaseChannel.cpp
@@ -3010,12 +3010,8 @@ HttpBaseChannel::SetupReplacementChannel(nsIURI       *newURI,
 
       NeckoOriginAttributes attrs = newLoadInfo->GetOriginAttributes();
 
-      MOZ_ASSERT(docShellAttrs.mAppId == attrs.mAppId,
-                "docshell and necko should have the same appId attribute.");
       MOZ_ASSERT(docShellAttrs.mUserContextId == attrs.mUserContextId,
                 "docshell and necko should have the same userContextId attribute.");
-      MOZ_ASSERT(docShellAttrs.mInIsolatedMozBrowser == attrs.mInIsolatedMozBrowser,
-                "docshell and necko should have the same inIsolatedMozBrowser attribute.");
       MOZ_ASSERT(docShellAttrs.mPrivateBrowsingId == attrs.mPrivateBrowsingId,
                  "docshell and necko should have the same privateBrowsingId attribute.");
 
diff --git a/uriloader/prefetch/OfflineCacheUpdateParent.cpp b/uriloader/prefetch/OfflineCacheUpdateParent.cpp
index 0381ec3f62..76edf35aac 100644
--- a/uriloader/prefetch/OfflineCacheUpdateParent.cpp
+++ b/uriloader/prefetch/OfflineCacheUpdateParent.cpp
@@ -256,20 +256,6 @@ OfflineCacheUpdateParent::SetRemoteTabs(bool aUseRemoteTabs)
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
-NS_IMETHODIMP
-OfflineCacheUpdateParent::GetIsInIsolatedMozBrowserElement(bool *aIsInIsolatedMozBrowserElement)
-{
-    NS_ENSURE_TRUE(mLoadingPrincipal, NS_ERROR_UNEXPECTED);
-    return mLoadingPrincipal->GetIsInIsolatedMozBrowserElement(aIsInIsolatedMozBrowserElement);
-}
-
-NS_IMETHODIMP
-OfflineCacheUpdateParent::GetAppId(uint32_t *aAppId)
-{
-    NS_ENSURE_TRUE(mLoadingPrincipal, NS_ERROR_UNEXPECTED);
-    return mLoadingPrincipal->GetAppId(aAppId);
-}
-
 NS_IMETHODIMP
 OfflineCacheUpdateParent::GetOriginAttributes(JS::MutableHandleValue aAttrs)
 {
diff --git a/uriloader/prefetch/nsIOfflineCacheUpdate.idl b/uriloader/prefetch/nsIOfflineCacheUpdate.idl
index 1308a8de27..87ec120bc9 100644
--- a/uriloader/prefetch/nsIOfflineCacheUpdate.idl
+++ b/uriloader/prefetch/nsIOfflineCacheUpdate.idl
@@ -224,9 +224,9 @@ interface nsIOfflineCacheUpdateService : nsISupports {
 
     /**
      * Schedule a cache update for a given offline manifest using app cache
-     * bound to the given appID+inIsolatedMozBrowser flag.  If an existing update
-     * is scheduled or running, that update will be returned. Otherwise a new
-     * update will be scheduled.
+     * bound to the given appID flag.  If an existing update is scheduled or
+     * running, that update will be returned. Otherwise a new update will be
+     * scheduled.
      */
     nsIOfflineCacheUpdate scheduleAppUpdate(in nsIURI aManifestURI,
                                             in nsIURI aDocumentURI,
diff --git a/xpfe/appshell/nsContentTreeOwner.cpp b/xpfe/appshell/nsContentTreeOwner.cpp
index 8e9a065a9c..18b9d5211e 100644
--- a/xpfe/appshell/nsContentTreeOwner.cpp
+++ b/xpfe/appshell/nsContentTreeOwner.cpp
@@ -820,7 +820,7 @@ nsContentTreeOwner::ProvideWindow(mozIDOMWindowProxy* aParent,
   // open a modal-type window, we're going to create a new <iframe mozbrowser>
   // and return its window here.
   nsCOMPtr<nsIDocShell> docshell = do_GetInterface(aParent);
-  if (docshell && docshell->GetIsInMozBrowserOrApp() &&
+  if (docshell && docshell->GetIsInMozBrowser() &&
       !(aChromeFlags & (nsIWebBrowserChrome::CHROME_MODAL |
                         nsIWebBrowserChrome::CHROME_OPENAS_DIALOG |
                         nsIWebBrowserChrome::CHROME_OPENAS_CHROME))) {