--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -1503,54 +1503,20 @@ nsGlobalWindow::WouldReuseInnerWindow(ns
     return itemType == nsIDocShellTreeItem::typeChrome;
   }
 
   // No treeItem: don't reuse the current inner window.
   return false;
 }
 
 void
-nsGlobalWindow::SetOpenerScriptPrincipal(nsIPrincipal* aPrincipal)
-{
-  FORWARD_TO_OUTER_VOID(SetOpenerScriptPrincipal, (aPrincipal));
-
-  if (mDoc) {
-    if (!mDoc->IsInitialDocument()) {
-      // We have a document already, and it's not the original one.  Bail out.
-      return;
-    }
-
-#ifdef DEBUG
-    // We better have an about:blank document loaded at this point.  Otherwise,
-    // something is really weird.
-    nsCOMPtr<nsIURI> uri;
-    mDoc->NodePrincipal()->GetURI(getter_AddRefs(uri));
-    NS_ASSERTION(uri && NS_IsAboutBlank(uri) &&
-                 NS_IsAboutBlank(mDoc->GetDocumentURI()),
-                 "Unexpected original document");
-#endif
-
-    GetDocShell()->CreateAboutBlankContentViewer(aPrincipal);
-    mDoc->SetIsInitialDocument(true);
-
-    nsCOMPtr<nsIPresShell> shell;
-    GetDocShell()->GetPresShell(getter_AddRefs(shell));
-
-    if (shell && !shell->DidInitialReflow()) {
-      // Ensure that if someone plays with this document they will get
-      // layout happening.
-      nsRect r = shell->GetPresContext()->GetVisibleArea();
-      shell->InitialReflow(r.width, r.height);
-    }
-  }
-}
-
-void
 nsGlobalWindow::SetInitialPrincipalToSubject()
 {
+  FORWARD_TO_OUTER_VOID(SetInitialPrincipalToSubject, ());
+
   // First, grab the subject principal. These methods never fail.
   nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
   nsCOMPtr<nsIPrincipal> newWindowPrincipal, systemPrincipal;
   ssm->GetSubjectPrincipal(getter_AddRefs(newWindowPrincipal));
   ssm->GetSystemPrincipal(getter_AddRefs(systemPrincipal));
   if (!newWindowPrincipal) {
     newWindowPrincipal = systemPrincipal;
   }
@@ -1561,18 +1527,48 @@ nsGlobalWindow::SetInitialPrincipalToSub
     int32_t itemType;
     nsCOMPtr<nsIDocShellTreeItem> item = do_QueryInterface(GetDocShell());
     nsresult rv = item->GetItemType(&itemType);
     if (NS_FAILED(rv) || itemType != nsIDocShellTreeItem::typeChrome) {
       newWindowPrincipal = nullptr;
     }
   }
 
-  // Set the initial about:blank document up with the correct principal.
-  SetOpenerScriptPrincipal(newWindowPrincipal);
+  // If there's an existing document, bail if it either:
+  if (mDoc) {
+    // (a) is not an initial about:blank document, or
+    if (!mDoc->IsInitialDocument())
+      return;
+    // (b) already has the correct principal.
+    if (mDoc->NodePrincipal() == newWindowPrincipal)
+      return;
+
+#ifdef DEBUG
+    // If we have a document loaded at this point, it had better be about:blank.
+    // Otherwise, something is really weird.
+    nsCOMPtr<nsIURI> uri;
+    mDoc->NodePrincipal()->GetURI(getter_AddRefs(uri));
+    NS_ASSERTION(uri && NS_IsAboutBlank(uri) &&
+                 NS_IsAboutBlank(mDoc->GetDocumentURI()),
+                 "Unexpected original document");
+#endif
+  }
+
+  GetDocShell()->CreateAboutBlankContentViewer(newWindowPrincipal);
+  mDoc->SetIsInitialDocument(true);
+
+  nsCOMPtr<nsIPresShell> shell;
+  GetDocShell()->GetPresShell(getter_AddRefs(shell));
+
+  if (shell && !shell->DidInitialReflow()) {
+    // Ensure that if someone plays with this document they will get
+    // layout happening.
+    nsRect r = shell->GetPresContext()->GetVisibleArea();
+    shell->InitialReflow(r.width, r.height);
+  }
 }
 
 PopupControlState
 PushPopupControlState(PopupControlState aState, bool aForce)
 {
   PopupControlState oldState = gPopupControlState;
 
   if (aState < gPopupControlState || aForce) {

--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -337,17 +337,16 @@ public:
 
   // nsPIDOMWindow
   virtual NS_HIDDEN_(nsPIDOMWindow*) GetPrivateRoot();
   virtual NS_HIDDEN_(void) ActivateOrDeactivate(bool aActivate);
   virtual NS_HIDDEN_(void) SetActive(bool aActive);
   virtual NS_HIDDEN_(void) SetIsBackground(bool aIsBackground);
   virtual NS_HIDDEN_(void) SetChromeEventHandler(nsIDOMEventTarget* aChromeEventHandler);
 
-  virtual NS_HIDDEN_(void) SetOpenerScriptPrincipal(nsIPrincipal* aPrincipal);
   virtual NS_HIDDEN_(void) SetInitialPrincipalToSubject();
 
   virtual NS_HIDDEN_(PopupControlState) PushPopupControlState(PopupControlState state, bool aForce) const;
   virtual NS_HIDDEN_(void) PopPopupControlState(PopupControlState state) const;
   virtual NS_HIDDEN_(PopupControlState) GetPopupControlState() const;
 
   virtual NS_HIDDEN_(nsresult) SaveWindowState(nsISupports **aState);
   virtual NS_HIDDEN_(nsresult) RestoreWindowState(nsISupports *aState);

--- a/dom/base/nsPIDOMWindow.h
+++ b/dom/base/nsPIDOMWindow.h
@@ -275,22 +275,18 @@ public:
       }
 
       win = this;
     }
 
     return win->mIsHandlingResizeEvent;
   }
 
-  // Tell this window who opened it.  This only has an effect if there is
-  // either no document currently in the window or if the document is the
-  // original document this window came with (an about:blank document either
-  // preloaded into it when it was created, or created by
-  // CreateAboutBlankContentViewer()).
-  virtual void SetOpenerScriptPrincipal(nsIPrincipal* aPrincipal) = 0;
+  // Set the window up with an about:blank document with the current subject
+  // principal.
   virtual void SetInitialPrincipalToSubject() = 0;
 
   virtual PopupControlState PushPopupControlState(PopupControlState aState,
                                                   bool aForce) const = 0;
   virtual void PopPopupControlState(PopupControlState state) const = 0;
   virtual PopupControlState GetPopupControlState() const = 0;
 
   // Returns an object containing the window's state.  This also suspends