diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 20c7275c15f0..eab678bc5089 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -10285,11 +10285,9 @@ nsGlobalWindow::GetSessionStorage(ErrorResult& aError)
       return nullptr;
     }
 
-    nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(docShell);
-
     nsCOMPtr<nsIDOMStorage> storage;
     aError = storageManager->CreateStorage(this, principal, documentURI,
-                                           loadContext && loadContext->UsePrivateBrowsing(),
+                                           IsPrivateBrowsing(),
                                            getter_AddRefs(storage));
     if (aError.Failed()) {
       return nullptr;
@@ -10365,12 +10363,9 @@ nsGlobalWindow::GetLocalStorage(ErrorResult& aError)
       mDoc->GetDocumentURI(documentURI);
     }
 
-    nsIDocShell* docShell = GetDocShell();
-    nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(docShell);
-
     nsCOMPtr<nsIDOMStorage> storage;
     aError = storageManager->CreateStorage(this, principal, documentURI,
-                                           loadContext && loadContext->UsePrivateBrowsing(),
+                                           IsPrivateBrowsing(),
                                            getter_AddRefs(storage));
     if (aError.Failed()) {
       return nullptr;
@@ -11200,9 +11195,7 @@ nsGlobalWindow::Observe(nsISupports* aSubject, const char* aTopic,
       return NS_OK;
     }
 
-    nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(GetDocShell());
-    bool isPrivate = loadContext && loadContext->UsePrivateBrowsing();
-    if (changingStorage->IsPrivate() != isPrivate) {
+    if (changingStorage->IsPrivate() != IsPrivateBrowsing()) {
       return NS_OK;
     }
 
@@ -12634,6 +12627,13 @@ nsGlobalWindow::SecurityCheckURL(const char *aURL)
   return NS_OK;
 }
 
+bool
+nsGlobalWindow::IsPrivateBrowsing()
+{
+  nsCOMPtr<nsILoadContext> loadContext = do_QueryInterface(GetDocShell());
+  return loadContext && loadContext->UsePrivateBrowsing();
+}
+
 void
 nsGlobalWindow::FlushPendingNotifications(mozFlushType aType)
 {
diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index dbc274e26e6b..067999f83714 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -1351,6 +1351,7 @@ public:
   already_AddRefed<nsIBaseWindow> GetTreeOwnerWindow();
   already_AddRefed<nsIWebBrowserChrome> GetWebBrowserChrome();
   nsresult SecurityCheckURL(const char *aURL);
+  bool IsPrivateBrowsing();
 
   bool PopupWhitelisted();
   PopupControlState RevisePopupAbuseLevel(PopupControlState);