--- a/accessible/windows/msaa/RootAccessibleWrap.cpp
+++ b/accessible/windows/msaa/RootAccessibleWrap.cpp
@@ -97,8 +97,52 @@ RootAccessibleWrap::DocumentActivated(Do
       HWND childDocHWND = static_cast<HWND>(childDoc->GetNativeWindow());
       if (childDoc != aDocument)
         nsWinUtils::HideNativeWindow(childDocHWND);
       else
         nsWinUtils::ShowNativeWindow(childDocHWND);
     }
   }
 }
+
+STDMETHODIMP
+RootAccessibleWrap::accNavigate(
+      /* [in] */ long navDir,
+      /* [optional][in] */ VARIANT varStart,
+      /* [retval][out] */ VARIANT __RPC_FAR *pvarEndUpAt)
+{
+  // Special handling for NAVRELATION_EMBEDS.
+  // When we only have a single process, this can be handled the same way as
+  // any other relation.
+  // However, for multi process, the normal relation mechanism doesn't work
+  // because it can't handle remote objects.
+  if (navDir != NAVRELATION_EMBEDS ||
+      varStart.vt != VT_I4  || varStart.lVal != CHILDID_SELF) {
+    // We only handle EMBEDS on the root here.
+    // Forward to the base implementation.
+    return DocAccessibleWrap::accNavigate(navDir, varStart, pvarEndUpAt);
+  }
+
+  if (!pvarEndUpAt) {
+    return E_INVALIDARG;
+  }
+
+  Accessible* target = nullptr;
+  // Get the document in the active tab.
+  ProxyAccessible* docProxy = GetPrimaryRemoteTopLevelContentDoc();
+  if (docProxy) {
+    target = WrapperFor(docProxy);
+  } else {
+    // The base implementation could handle this, but we may as well
+    // just handle it here.
+    Relation rel = RelationByType(RelationType::EMBEDS);
+    target = rel.Next();
+  }
+
+  if (!target) {
+    return E_FAIL;
+  }
+
+  VariantInit(pvarEndUpAt);
+  pvarEndUpAt->pdispVal = NativeAccessible(target);
+  pvarEndUpAt->vt = VT_DISPATCH;
+  return S_OK;
+}

--- a/accessible/windows/msaa/RootAccessibleWrap.h
+++ b/accessible/windows/msaa/RootAccessibleWrap.h
@@ -33,16 +33,21 @@ public:
   already_AddRefed<IUnknown> Aggregate(IUnknown* aOuter);
 
   /**
    * @return This object's own IUnknown, as opposed to its wrapper's IUnknown
    *         which is what would be returned by QueryInterface(IID_IUnknown).
    */
   already_AddRefed<IUnknown> GetInternalUnknown();
 
+  virtual /* [id] */ HRESULT STDMETHODCALLTYPE accNavigate(
+    /* [in] */ long navDir,
+    /* [optional][in] */ VARIANT varStart,
+    /* [retval][out] */ VARIANT __RPC_FAR *pvarEndUpAt) override;
+
 private:
   // DECLARE_AGGREGATABLE declares the internal IUnknown methods as well as
   // mInternalUnknown.
   DECLARE_AGGREGATABLE(RootAccessibleWrap);
   IUnknown* mOuter;
 };
 
 } // namespace a11y