--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -887,125 +887,16 @@ Navigator::RegisterProtocolHandler(const
   if (!registrar) {
     return;
   }
 
   aRv = registrar->RegisterProtocolHandler(aProtocol, aURI, aTitle,
                                            mWindow->GetOuterWindow());
 }
 
-bool
-Navigator::MozIsLocallyAvailable(const nsAString &aURI,
-                                 bool aWhenOffline,
-                                 ErrorResult& aRv)
-{
-  nsCOMPtr<nsIURI> uri;
-  nsresult rv = NS_NewURI(getter_AddRefs(uri), aURI);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  // This method of checking the cache will only work for http/https urls.
-  bool match;
-  rv = uri->SchemeIs("http", &match);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  if (!match) {
-    rv = uri->SchemeIs("https", &match);
-    if (NS_FAILED(rv)) {
-      aRv.Throw(rv);
-      return false;
-    }
-    if (!match) {
-      aRv.Throw(NS_ERROR_DOM_BAD_URI);
-      return false;
-    }
-  }
-
-  // Same origin check.
-  JSContext *cx = nsContentUtils::GetCurrentJSContext();
-  if (!cx) {
-    aRv.Throw(NS_ERROR_FAILURE);
-    return false;
-  }
-
-  rv = nsContentUtils::GetSecurityManager()->CheckSameOrigin(cx, uri);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  // These load flags cause an error to be thrown if there is no
-  // valid cache entry, and skip the load if there is.
-  // If the cache is busy, assume that it is not yet available rather
-  // than waiting for it to become available.
-  uint32_t loadFlags = nsIChannel::INHIBIT_CACHING |
-                       nsICachingChannel::LOAD_NO_NETWORK_IO |
-                       nsICachingChannel::LOAD_ONLY_IF_MODIFIED |
-                       nsICachingChannel::LOAD_BYPASS_LOCAL_CACHE_IF_BUSY;
-
-  if (aWhenOffline) {
-    loadFlags |= nsICachingChannel::LOAD_CHECK_OFFLINE_CACHE |
-                 nsICachingChannel::LOAD_ONLY_FROM_CACHE |
-                 nsIRequest::LOAD_FROM_CACHE;
-  }
-
-  if (!mWindow) {
-    aRv.Throw(NS_ERROR_UNEXPECTED);
-    return false;
-  }
-
-  nsCOMPtr<nsILoadGroup> loadGroup;
-  nsCOMPtr<nsIDocument> doc = mWindow->GetDoc();
-  if (doc) {
-    loadGroup = doc->GetDocumentLoadGroup();
-  }
-
-  nsCOMPtr<nsIChannel> channel;
-  rv = NS_NewChannel(getter_AddRefs(channel), uri,
-                     nullptr, loadGroup, nullptr, loadFlags);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  nsCOMPtr<nsIInputStream> stream;
-  rv = channel->Open(getter_AddRefs(stream));
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  stream->Close();
-
-  nsresult status;
-  rv = channel->GetStatus(&status);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-
-  if (NS_FAILED(status)) {
-    return false;
-  }
-
-  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(channel);
-  bool isAvailable;
-  rv = httpChannel->GetRequestSucceeded(&isAvailable);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-    return false;
-  }
-  return isAvailable;
-}
-
 nsDOMDeviceStorage*
 Navigator::GetDeviceStorage(const nsAString& aType, ErrorResult& aRv)
 {
   if (!mWindow || !mWindow->GetOuterWindow() || !mWindow->GetDocShell()) {
     aRv.Throw(NS_ERROR_FAILURE);
     return nullptr;
   }
 

--- a/dom/base/Navigator.h
+++ b/dom/base/Navigator.h
@@ -202,18 +202,16 @@ public:
   already_AddRefed<WakeLock> RequestWakeLock(const nsAString &aTopic,
                                              ErrorResult& aRv);
   nsDOMDeviceStorage* GetDeviceStorage(const nsAString& aType,
                                        ErrorResult& aRv);
   void GetDeviceStorages(const nsAString& aType,
                          nsTArray<nsRefPtr<nsDOMDeviceStorage> >& aStores,
                          ErrorResult& aRv);
   DesktopNotificationCenter* GetMozNotification(ErrorResult& aRv);
-  bool MozIsLocallyAvailable(const nsAString& aURI, bool aWhenOffline,
-                             ErrorResult& aRv);
   MobileMessageManager* GetMozMobileMessage();
   Telephony* GetMozTelephony(ErrorResult& aRv);
   network::Connection* GetConnection(ErrorResult& aRv);
   nsDOMCameraManager* GetMozCameras(ErrorResult& aRv);
   void MozSetMessageHandler(const nsAString& aType,
                             systemMessageCallback* aCallback,
                             ErrorResult& aRv);
   bool MozHasPendingMessage(const nsAString& aType, ErrorResult& aRv);

--- a/dom/webidl/Navigator.webidl
+++ b/dom/webidl/Navigator.webidl
@@ -248,22 +248,16 @@ partial interface Navigator {
 };
 
 // nsIDOMNavigatorDesktopNotification
 partial interface Navigator {
   [Throws, Pref="notification.feature.enabled"]
   readonly attribute DesktopNotificationCenter mozNotification;
 };
 
-// nsIDOMClientInformation
-partial interface Navigator {
-  [Throws]
-  boolean mozIsLocallyAvailable(DOMString uri, boolean whenOffline);
-};
-
 #ifdef MOZ_WEBSMS_BACKEND
 partial interface Navigator {
   [CheckPermissions="sms", Pref="dom.sms.enabled"]
   readonly attribute MozMobileMessageManager? mozMobileMessage;
 };
 #endif
 
 // NetworkInformation