diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index e7e35849c3f..9f690678aff 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -16,6 +16,7 @@
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/TabChild.h"
 #include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "mozilla/dom/ScreenOrientation.h"
 #include "mozilla/dom/ToJSValue.h"
 #include "mozilla/dom/workers/ServiceWorkerManager.h"
 #include "mozilla/EventStateManager.h"
@@ -754,6 +755,7 @@ nsDocShell::nsDocShell()
   , mLoadedTransIndex(-1)
   , mSandboxFlags(0)
   , mFullscreenAllowed(CHECK_ATTRIBUTES)
+  , mOrientationLock(eScreenOrientation_None)
   , mCreated(false)
   , mAllowSubframes(true)
   , mAllowPlugins(true)
@@ -2548,6 +2550,18 @@ nsDocShell::SetFullscreenAllowed(bool aFullscreenAllowed)
   return NS_OK;
 }
 
+ScreenOrientationInternal
+nsDocShell::OrientationLock()
+{
+  return mOrientationLock;
+}
+
+void
+nsDocShell::SetOrientationLock(ScreenOrientationInternal aOrientationLock)
+{
+  mOrientationLock = aOrientationLock;
+}
+
 NS_IMETHODIMP
 nsDocShell::GetMayEnableCharacterEncodingMenu(
     bool* aMayEnableCharacterEncodingMenu)
@@ -5921,6 +5935,16 @@ nsDocShell::SetIsActive(bool aIsActive)
   if (mScriptGlobal) {
     mScriptGlobal->SetIsBackground(!aIsActive);
     if (nsCOMPtr<nsIDocument> doc = mScriptGlobal->GetExtantDoc()) {
+      if (aIsActive) {
+        nsCOMPtr<nsIDocShellTreeItem> parent;
+        GetSameTypeParent(getter_AddRefs(parent));
+        if (!parent) {
+          // We only care about the top-level browsing context.
+          uint16_t orientation = OrientationLock();
+          ScreenOrientation::UpdateActiveOrientationLock(orientation);
+        }
+      }
+
       doc->PostVisibilityUpdateEvent();
     }
   }
@@ -10042,6 +10066,22 @@ nsDocShell::InternalLoad(nsIURI* aURI,
     mTiming->NotifyUnloadAccepted(mCurrentURI);
   }
 
+  // Whenever a top-level browsing context is navigated, the user agent MUST
+  // 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.
+  if (OrientationLock() != eScreenOrientation_None) {
+#ifdef DEBUG
+    nsCOMPtr<nsIDocShellTreeItem> parent;
+    GetSameTypeParent(getter_AddRefs(parent));
+    MOZ_ASSERT(!parent);
+#endif
+    SetOrientationLock(eScreenOrientation_None);
+    if (mIsActive) {
+      ScreenOrientation::UpdateActiveOrientationLock(eScreenOrientation_None);
+    }
+  }
+
   // Check for saving the presentation here, before calling Stop().
   // This is necessary so that we can catch any pending requests.
   // Since the new request has not been created yet, we pass null for the
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index ba23b371d66..992b4582c59 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -62,6 +62,7 @@
 namespace mozilla {
 namespace dom {
 class EventTarget;
+typedef uint32_t ScreenOrientationInternal;
 } // namespace dom
 } // namespace mozilla
 
@@ -875,6 +876,10 @@ protected:
   };
   FullscreenAllowedState mFullscreenAllowed;
 
+  // The orientation lock as described by
+  // https://w3c.github.io/screen-orientation/
+  mozilla::dom::ScreenOrientationInternal mOrientationLock;
+
   // Cached value of the "browser.xul.error_pages.enabled" preference.
   static bool sUseErrorPages;
 
diff --git a/docshell/base/nsIDocShell.idl b/docshell/base/nsIDocShell.idl
index b216c13c0f3..d637791f5ae 100644
--- a/docshell/base/nsIDocShell.idl
+++ b/docshell/base/nsIDocShell.idl
@@ -46,7 +46,7 @@ interface nsITabParent;
  
 typedef unsigned long nsLoadFlags;
 
-[scriptable, builtinclass, uuid(97471054-0BC8-4A57-BBFE-6C255BCBBB67)]
+[scriptable, builtinclass, uuid(35a26f70-dbb9-450d-b634-cd0bbb9b8e13)]
 interface nsIDocShell : nsIDocShellTreeItem
 {
   /**
@@ -926,6 +926,9 @@ interface nsIDocShell : nsIDocShellTreeItem
   
   void setFullscreenAllowed(in boolean allowed);
 
+  [notxpcom] uint32_t orientationLock();
+  [notxpcom] void setOrientationLock(in uint32_t orientationLock);
+
   [noscript, infallible] attribute boolean affectPrivateSessionLifetime;
 
   /**
diff --git a/dom/base/ScreenOrientation.cpp b/dom/base/ScreenOrientation.cpp
index 7dacd18ecbd..ca24ca57fab 100644
--- a/dom/base/ScreenOrientation.cpp
+++ b/dom/base/ScreenOrientation.cpp
@@ -317,6 +317,7 @@ ScreenOrientation::LockInternal(ScreenOrientationInternal aOrientation, ErrorRes
     return nullptr;
   }
 
+  rootShell->SetOrientationLock(aOrientation);
   AbortOrientationPromises(rootShell);
 
   doc->SetOrientationPendingPromise(p);
@@ -530,6 +531,16 @@ ScreenOrientation::Notify(const hal::ScreenConfiguration& aConfiguration)
   }
 }
 
+void
+ScreenOrientation::UpdateActiveOrientationLock(ScreenOrientationInternal aOrientation)
+{
+  if (aOrientation == eScreenOrientation_None) {
+    hal::UnlockScreenOrientation();
+  } else {
+    hal::LockScreenOrientation(aOrientation);
+  }
+}
+
 void
 ScreenOrientation::DispatchChangeEvent()
 {
diff --git a/dom/base/ScreenOrientation.h b/dom/base/ScreenOrientation.h
index a7fcbd19d69..796cb9a9bd9 100644
--- a/dom/base/ScreenOrientation.h
+++ b/dom/base/ScreenOrientation.h
@@ -63,6 +63,8 @@ public:
 
   void Notify(const mozilla::hal::ScreenConfiguration& aConfiguration) override;
 
+  static void UpdateActiveOrientationLock(ScreenOrientationInternal aOrientation);
+
 private:
   virtual ~ScreenOrientation();