diff --git a/dom/base/DocGroup.cpp b/dom/base/DocGroup.cpp
deleted file mode 100644
index 0ab3ff90fb40..000000000000
--- a/dom/base/DocGroup.cpp
+++ /dev/null
@@ -1,81 +0,0 @@
-#include "mozilla/dom/DocGroup.h"
-#include "nsIURI.h"
-#include "nsIEffectiveTLDService.h"
-
-namespace mozilla {
-namespace dom {
-
-/* static */ void
-DocGroup::GetKey(nsIPrincipal* aPrincipal, nsACString& aKey)
-{
-  aKey.Truncate();
-  nsCOMPtr<nsIURI> uri;
-  nsresult rv = aPrincipal->GetURI(getter_AddRefs(uri));
-  if (NS_SUCCEEDED(rv)) {
-    nsCOMPtr<nsIEffectiveTLDService> tldService =
-      do_GetService(NS_EFFECTIVETLDSERVICE_CONTRACTID);
-    if (tldService) {
-      rv = tldService->GetBaseDomain(uri, 0, aKey);
-      if (NS_FAILED(rv)) {
-        aKey.Truncate();
-      }
-    }
-  }
-}
-
-void
-DocGroup::Remove(nsPIDOMWindowInner* aWindow)
-{
-  MOZ_ASSERT(mWindows.Contains(aWindow));
-  mWindows.RemoveElement(aWindow);
-}
-
-DocGroup::DocGroup(TabGroup* aTabGroup, const nsACString& aKey)
-  : mKey(aKey), mTabGroup(aTabGroup)
-{
-  // This method does not add itself to mTabGroup->mDocGroups as the caller does it for us
-}
-
-DocGroup::~DocGroup()
-{
-  MOZ_ASSERT(mWindows.IsEmpty());
-  mTabGroup->mDocGroups.RemoveEntry(mKey);
-}
-
-TabGroup::~TabGroup()
-{
-  MOZ_ASSERT(mDocGroups.IsEmpty());
-}
-
-already_AddRefed<DocGroup>
-TabGroup::GetDocGroup(const nsACString& aKey)
-{
-  RefPtr<DocGroup> docGroup(mDocGroups.GetEntry(aKey)->mDocGroup);
-  return docGroup.forget();
-}
-
-already_AddRefed<DocGroup>
-TabGroup::JoinDocGroup(const nsACString& aKey, nsPIDOMWindowInner* aWindow)
-{
-  HashEntry* entry = mDocGroups.PutEntry(aKey);
-  RefPtr<DocGroup> docGroup;
-  if (entry->mDocGroup) {
-    docGroup = entry->mDocGroup;
-  } else {
-    docGroup = new DocGroup(this, aKey);
-    entry->mDocGroup = docGroup;
-  }
-
-  // Make sure that the hashtable was updated and now contains the correct value
-  MOZ_ASSERT(RefPtr<DocGroup>(GetDocGroup(aKey)) == docGroup);
-
-  docGroup->mWindows.AppendElement(aWindow);
-  return docGroup.forget();
-}
-
-TabGroup::HashEntry::HashEntry(const nsACString* aKey)
-  : nsCStringHashKey(aKey), mDocGroup(nullptr)
-{}
-
-}
-}
diff --git a/dom/base/DocGroup.h b/dom/base/DocGroup.h
deleted file mode 100644
index 0d5ef14461a7..000000000000
--- a/dom/base/DocGroup.h
+++ /dev/null
@@ -1,115 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this file,
- * You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef DocGroup_h
-#define DocGroup_h
-
-#include "nsISupports.h"
-#include "nsISupportsImpl.h"
-#include "nsIPrincipal.h"
-#include "nsTHashtable.h"
-#include "nsString.h"
-
-#include "mozilla/RefPtr.h"
-
-namespace mozilla {
-namespace dom {
-
-// Two browsing contexts are considered "related" if they are reachable from one
-// another through window.opener, window.parent, or window.frames. This is the
-// spec concept of a "unit of related browsing contexts"
-//
-// Two browsing contexts are considered "similar-origin" if they can be made to
-// have the same origin by setting document.domain. This is the spec concept of
-// a "unit of similar-origin related browsing contexts"
-//
-// A TabGroup is a set of browsing contexts which are all "related". Within a
-// TabGroup, browsing contexts are broken into "similar-origin" DocGroups. In
-// more detail, a DocGroup is actually a collection of inner windows, and a
-// TabGroup is a collection of DocGroups. A TabGroup typically will contain
-// (through its DocGroups) the inner windows from one or more tabs related by
-// window.opener. A DocGroup is a member of exactly one TabGroup. Inner windows
-// that aren't the current window of an outer window are not part of any
-// DocGroup.
-
-class TabGroup;
-
-class DocGroup {
-private:
-  typedef nsTArray<nsPIDOMWindowInner*> WindowArray;
-public:
-  typedef WindowArray::iterator Iterator;
-
-  friend class TabGroup;
-  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(DocGroup)
-
-  static void GetKey(nsIPrincipal* aPrincipal, nsACString& aString);
-  bool MatchesKey(const nsACString& aKey) {
-    return aKey == mKey;
-  }
-  TabGroup* GetTabGroup() {
-    return mTabGroup;
-  }
-  void Remove(nsPIDOMWindowInner* aWindow);
-
-  // Iterators for iterating over every window within the DocGroup
-  Iterator begin() {
-    return mWindows.begin();
-  }
-  Iterator end() {
-    return mWindows.end();
-  }
-
-private:
-  DocGroup(TabGroup* aTabGroup, const nsACString& aKey);
-  ~DocGroup();
-
-  nsCString mKey;
-  RefPtr<TabGroup> mTabGroup;
-  WindowArray mWindows;
-};
-
-
-class TabGroup {
-private:
-  class HashEntry : public nsCStringHashKey {
-  public:
-    // NOTE: Weak reference. The DocGroup destructor removes itself from itw
-    // owning TabGroup.
-    DocGroup* mDocGroup;
-    explicit HashEntry(const nsACString* aKey);
-  };
-
-  typedef nsTHashtable<HashEntry> DocGroupMap;
-public:
-  typedef DocGroupMap::Iterator Iterator;
-
-  friend class DocGroup;
-  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(TabGroup)
-
-  TabGroup() {}
-
-  // Get the docgroup for the corresponding doc group key.
-  // Returns null if the given key hasn't been seen yet.
-  already_AddRefed<DocGroup>
-  GetDocGroup(const nsACString& aKey);
-
-  already_AddRefed<DocGroup>
-  JoinDocGroup(const nsACString& aKey, nsPIDOMWindowInner* aWindow);
-
-  Iterator Iter() {
-    return mDocGroups.Iter();
-  }
-
-private:
-  ~TabGroup();
-  DocGroupMap mDocGroups;
-};
-
-} // namespace dom
-} // namespace mozilla
-
-#endif // defined(DocGroup_h)
diff --git a/dom/base/FormData.cpp b/dom/base/FormData.cpp
index 6095286be97d..aba7afc1e467 100644
--- a/dom/base/FormData.cpp
+++ b/dom/base/FormData.cpp
@@ -8,7 +8,6 @@
 #include "nsIVariant.h"
 #include "nsIInputStream.h"
 #include "mozilla/dom/File.h"
-#include "mozilla/dom/Directory.h"
 #include "mozilla/dom/HTMLFormElement.h"
 
 #include "MultipartBlobImpl.h"
diff --git a/dom/base/moz.build b/dom/base/moz.build
index 6563e5a6f9e0..114635f2b5c6 100644
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -159,7 +159,6 @@ EXPORTS.mozilla.dom += [
     'Comment.h',
     'CustomElementsRegistry.h',
     'DirectionalityUtils.h',
-    'DocGroup.h',
     'DocumentFragment.h',
     'DocumentType.h',
     'DOMCursor.h',
@@ -223,7 +222,6 @@ UNIFIED_SOURCES += [
     'Crypto.cpp',
     'CustomElementsRegistry.cpp',
     'DirectionalityUtils.cpp',
-    'DocGroup.cpp',
     'DocumentFragment.cpp',
     'DocumentType.cpp',
     'DOMCursor.cpp',
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index aad64d77d49f..5c8e2c5af88c 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -80,7 +80,6 @@
 #include "nsAboutProtocolUtils.h"
 #include "nsCharTraits.h" // NS_IS_HIGH/LOW_SURROGATE
 #include "PostMessageEvent.h"
-#include "DocGroup.h"
 
 // Interfaces Needed
 #include "nsIFrame.h"
@@ -1227,7 +1226,8 @@ nsGlobalWindow::nsGlobalWindow(nsGlobalWindow *aOuterWindow)
     mDialogAbuseCount(0),
     mAreDialogsEnabled(true),
     mCanSkipCCGeneration(0),
-    mTabGroup(new TabGroup())
+    mStaticConstellation(0),
+    mConstellation(NullCString())
 {
   AssertIsOnMainThread();
 
@@ -1262,6 +1262,11 @@ nsGlobalWindow::nsGlobalWindow(nsGlobalWindow *aOuterWindow)
     // remain frozen until they get an inner window, so freeze this
     // outer window here.
     Freeze();
+
+    // As an outer window, we may be the root of a constellation. This initial
+    // static constellation may be overridden as this window is given a parent
+    // window or an opener.
+    mStaticConstellation = WindowID();
   }
 
   // We could have failed the first time through trying
@@ -1425,12 +1430,6 @@ nsGlobalWindow::~nsGlobalWindow()
     }
   }
 
-  // Ensure that the docgroup doesn't hold a now-dead reference to our window
-  if (mDocGroup) {
-    MOZ_ASSERT(IsInnerWindow());
-    mDocGroup->Remove(AsInner());
-  }
-
   // Outer windows are always supposed to call CleanUp before letting themselves
   // be destroyed. And while CleanUp generally seems to be intended to clean up
   // outers, we've historically called it for both. Changing this would probably
@@ -3015,9 +3014,6 @@ nsGlobalWindow::InnerSetNewDocument(JSContext* aCx, nsIDocument* aDocument)
   mLocalStorage = nullptr;
   mSessionStorage = nullptr;
 
-  // Change which DocGroup this InnerWindow is in.
-  SwitchDocGroup();
-
 #ifdef DEBUG
   mLastOpenedURI = aDocument->GetDocumentURI();
 #endif
@@ -3041,9 +3037,10 @@ nsGlobalWindow::SetDocShell(nsIDocShell* aDocShell)
 
   mDocShell = aDocShell; // Weak Reference
 
+  // Copy over the static constellation from our new parent.
   nsCOMPtr<nsPIDOMWindowOuter> parentWindow = GetParent();
   if (parentWindow) {
-    InheritTabGroupFrom(parentWindow);
+    mStaticConstellation = Cast(parentWindow)->mStaticConstellation;
   }
 
   NS_ASSERTION(!mNavigator, "Non-null mNavigator in outer window!");
@@ -3157,8 +3154,9 @@ nsGlobalWindow::SetOpenerWindow(nsPIDOMWindowOuter* aOpener,
   mOpener = do_GetWeakReference(aOpener);
   NS_ASSERTION(mOpener || !aOpener, "Opener must support weak references!");
 
+  // Copy over the static constellation from our new opener
   if (aOpener) {
-    InheritTabGroupFrom(aOpener);
+    mStaticConstellation = Cast(aOpener)->mStaticConstellation;
   }
 
   if (aOriginalOpener) {
@@ -14413,74 +14411,44 @@ nsGlobalWindow::CheckForDPIChange()
   }
 }
 
-TabGroup*
-nsGlobalWindow::GetTabGroup()
-{
-  FORWARD_TO_OUTER(GetTabGroup, (), nullptr);
-
-#ifdef DEBUG
-  // Sanity check that our tabgroup matches our opener or parent
-  RefPtr<nsGlobalWindow> top = GetTopInternal();
-  RefPtr<nsPIDOMWindowOuter> opener = GetOpener();
-  MOZ_ASSERT_IF(top, top->mTabGroup == mTabGroup);
-  MOZ_ASSERT_IF(opener, Cast(opener)->mTabGroup == mTabGroup);
-#endif
-
-  return mTabGroup;
-}
-
-DocGroup*
-nsGlobalWindow::GetDocGroup()
-{
-  FORWARD_TO_INNER(GetDocGroup, (), nullptr);
-
-#ifdef DEBUG
-  // Sanity check that we have an up-to-date and accurate docgroup
-  if (mDocGroup) {
-    nsAutoCString docGroupKey;
-    DocGroup::GetKey(GetPrincipal(), docGroupKey);
-    MOZ_ASSERT(mDocGroup->MatchesKey(docGroupKey));
-    MOZ_ASSERT(mDocGroup->GetTabGroup() == GetTabGroup());
-  }
-#endif
-
-  return mDocGroup;
-}
-
 void
-nsGlobalWindow::SwitchDocGroup()
+nsGlobalWindow::GetConstellation(nsACString& aConstellation)
 {
-  MOZ_RELEASE_ASSERT(IsInnerWindow() && mTabGroup);
-  nsAutoCString docGroupKey;
-  DocGroup::GetKey(GetPrincipal(), docGroupKey);
+  FORWARD_TO_INNER_VOID(GetConstellation, (aConstellation));
 
-  if (mDocGroup) {
-    if (mDocGroup->MatchesKey(docGroupKey)) {
-      return;
+#ifdef DEBUG
+  RefPtr<nsGlobalWindow> outer = GetOuterWindowInternal();
+  MOZ_ASSERT(outer, "We should have an outer window");
+  RefPtr<nsGlobalWindow> top = outer->GetTopInternal();
+  RefPtr<nsPIDOMWindowOuter> opener = outer->GetOpener();
+  MOZ_ASSERT(!top || (top->mStaticConstellation ==
+                      outer->mStaticConstellation));
+  MOZ_ASSERT(!opener || (Cast(opener)->mStaticConstellation ==
+                         outer->mStaticConstellation));
+#endif
+
+  if (mConstellation.IsVoid()) {
+    mConstellation.Truncate();
+    // The dynamic constellation part comes from the eTLD+1 for the principal's URI.
+    nsCOMPtr<nsIPrincipal> principal = GetPrincipal();
+    nsCOMPtr<nsIURI> uri;
+    nsresult rv = principal->GetURI(getter_AddRefs(uri));
+    if (NS_SUCCEEDED(rv)) {
+      nsCOMPtr<nsIEffectiveTLDService> tldService =
+        do_GetService(NS_EFFECTIVETLDSERVICE_CONTRACTID);
+      if (tldService) {
+        rv = tldService->GetBaseDomain(uri, 0, mConstellation);
+        if (NS_FAILED(rv)) {
+          mConstellation.Truncate();
+        }
+      }
     }
-    MOZ_CRASH("The docgroup of an inner window should not change");
-  }
-  mDocGroup = GetTabGroup()->JoinDocGroup(docGroupKey, AsInner());
-}
 
-void
-nsGlobalWindow::InheritTabGroupFrom(nsPIDOMWindowOuter* aWindow)
-{
-  MOZ_RELEASE_ASSERT(IsOuterWindow());
-  // If we have an inner window, then that inner window's current doc group is
-  // within our current tab group. As we are inheriting our tab group (and thus
-  // changing away from the default of having a new tab group per window), we
-  // need to remove that inner window from its doc group before we switch to the
-  // new tab group.
-  RefPtr<nsGlobalWindow> inner = GetCurrentInnerWindowInternal();
-  if (inner) {
-    inner->mDocGroup->Remove(inner->AsInner());
-    inner->mDocGroup = nullptr;
-  }
-  mTabGroup = Cast(aWindow)->mTabGroup;
-  if (inner) {
-    inner->SwitchDocGroup();
+    // Get the static constellation from the outer window object.
+    mConstellation.AppendPrintf("^%llu", GetOuterWindowInternal()->mStaticConstellation);
   }
+
+  aConstellation.Assign(mConstellation);
 }
 
 nsGlobalWindow::TemporarilyDisableDialogs::TemporarilyDisableDialogs(
diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index 12e2d18d2c6d..3b1e6dd4983f 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -106,7 +106,6 @@ struct ChannelPixelLayout;
 class Console;
 class Crypto;
 class CustomElementsRegistry;
-class DocGroup;
 class External;
 class Function;
 class Gamepad;
@@ -122,7 +121,6 @@ struct RequestInit;
 class RequestOrUSVString;
 class Selection;
 class SpeechSynthesis;
-class TabGroup;
 class U2F;
 class VRDisplay;
 class VREventObserver;
@@ -1711,14 +1709,9 @@ private:
   // IsSecureContext() for the inner window that corresponds to aDocument.
   bool ComputeIsSecureContext(nsIDocument* aDocument);
 
-  // Called on inner/outer windows to update the current doc/tab group
-  void InheritTabGroupFrom(nsPIDOMWindowOuter* aWindow); // Outer only
-  void SwitchDocGroup(); // Inner only
-
 public:
 
-  mozilla::dom::TabGroup* GetTabGroup();
-  mozilla::dom::DocGroup* GetDocGroup();
+  void GetConstellation(nsACString& aConstellation);
 
 protected:
   // This member is also used on both inner and outer windows, but
@@ -1937,8 +1930,8 @@ protected:
 
   nsAutoPtr<mozilla::dom::VREventObserver> mVREventObserver;
 
-  RefPtr<mozilla::dom::DocGroup> mDocGroup; // Inner window only
-  RefPtr<mozilla::dom::TabGroup> mTabGroup; // Outer window only
+  uint64_t mStaticConstellation; // Only used on outer windows
+  nsCString mConstellation; // Only used on inner windows
 
   friend class nsDOMScriptableHelper;
   friend class nsDOMWindowUtils;