diff --git a/accessible/windows/ia2/ia2Accessible.cpp b/accessible/windows/ia2/ia2Accessible.cpp
index 0a4eb5d41531..a18012649902 100644
--- a/accessible/windows/ia2/ia2Accessible.cpp
+++ b/accessible/windows/ia2/ia2Accessible.cpp
@@ -495,7 +495,7 @@ ia2Accessible::get_uniqueID(long* aUniqueID)
     return E_INVALIDARG;
 
   AccessibleWrap* acc = static_cast<AccessibleWrap*>(this);
-  *aUniqueID = - reinterpret_cast<intptr_t>(acc->UniqueID());
+  *aUniqueID = AccessibleWrap::GetChildIDFor(acc);
   return S_OK;
 
   A11Y_TRYBLOCK_END
diff --git a/accessible/windows/msaa/AccessibleWrap.cpp b/accessible/windows/msaa/AccessibleWrap.cpp
index 05e4f958dcd5..bfacdfd1f217 100644
--- a/accessible/windows/msaa/AccessibleWrap.cpp
+++ b/accessible/windows/msaa/AccessibleWrap.cpp
@@ -56,16 +56,48 @@ const uint32_t USE_ROLE_STRING = 0;
 static gAccessibles = 0;
 #endif
 
+#ifdef _WIN64
+IDSet AccessibleWrap::sIDGen;
+
+static const uint32_t kNoID = 0;
+#endif
+
 static const int32_t kIEnumVariantDisconnected = -1;
 
 ////////////////////////////////////////////////////////////////////////////////
 // AccessibleWrap
 ////////////////////////////////////////////////////////////////////////////////
+AccessibleWrap::AccessibleWrap(nsIContent* aContent, DocAccessible* aDoc) :
+  Accessible(aContent, aDoc)
+#ifdef _WIN64
+  , mID(kNoID)
+#endif
+{
+}
+
+AccessibleWrap::~AccessibleWrap()
+{
+#ifdef _WIN64
+  if (mID != kNoID)
+    sIDGen.ReleaseID(mID);
+#endif
+}
 
 ITypeInfo* AccessibleWrap::gTypeInfo = nullptr;
 
 NS_IMPL_ISUPPORTS_INHERITED0(AccessibleWrap, Accessible)
 
+void
+AccessibleWrap::Shutdown()
+{
+#ifdef _WIN64
+  if (mID != kNoID)
+    static_cast<DocAccessibleWrap*>(mDoc)->RemoveID(mID);
+#endif
+
+  Accessible::Shutdown();
+}
+
 //-----------------------------------------------------
 // IUnknown interface methods - see iunknown.h for documentation
 //-----------------------------------------------------
@@ -1254,10 +1286,23 @@ AccessibleWrap::GetChildIDFor(Accessible* aAccessible)
   // so that the 3rd party application can call back and get the IAccessible
   // the event occurred on.
 
-  // Yes, this means we're only compatibible with 32 bit
-  // MSAA is only available for 32 bit windows, so it's okay
-  // XXX: bug 606080
-  return aAccessible ? - NS_PTR_TO_INT32(aAccessible->UniqueID()) : 0;
+#ifdef _WIN64
+  if (!aAccessible || !aAccessible->Document())
+    return 0;
+
+  uint32_t* id = & static_cast<AccessibleWrap*>(aAccessible)->mID;
+  if (*id != kNoID)
+    return *id;
+
+  *id = sIDGen.GetID();
+  DocAccessibleWrap* doc =
+    static_cast<DocAccessibleWrap*>(aAccessible->Document());
+  doc->AddID(*id, static_cast<AccessibleWrap*>(aAccessible));
+
+  return *id;
+#else
+  return - reinterpret_cast<intptr_t>(aAccessible);
+#endif
 }
 
 HWND
@@ -1307,6 +1352,25 @@ AccessibleWrap::NativeAccessible(Accessible* aAccessible)
   return static_cast<IDispatch*>(msaaAccessible);
 }
 
+#ifdef _WIN64
+static Accessible*
+GetAccessibleInSubtree(DocAccessible* aDoc, uint32_t aID)
+{
+  Accessible* child = static_cast<DocAccessibleWrap*>(aDoc)->GetAccessibleByID(aID);
+  if (child)
+    return child;
+
+  uint32_t childDocCount = aDoc->ChildDocumentCount();
+  for (uint32_t i = 0; i < childDocCount; i++) {
+    child = GetAccessibleInSubtree(aDoc->GetChildDocumentAt(i), aID);
+    if (child)
+      return child;
+  }
+
+    return nullptr;
+  }
+#endif
+
 Accessible*
 AccessibleWrap::GetXPAccessibleFor(const VARIANT& aVarChild)
 {
@@ -1342,7 +1406,11 @@ AccessibleWrap::GetXPAccessibleFor(const VARIANT& aVarChild)
 
     DocAccessible* document = Document();
     Accessible* child =
+#ifdef _WIN64
+    GetAccessibleInSubtree(document, static_cast<uint32_t>(aVarChild.lVal));
+#else
       document->GetAccessibleByUniqueIDInSubtree(uniqueID);
+#endif
 
     // If it is a document then just return an accessible.
     if (IsDoc())
diff --git a/accessible/windows/msaa/AccessibleWrap.h b/accessible/windows/msaa/AccessibleWrap.h
index b32ede032c22..a3d730f927d8 100644
--- a/accessible/windows/msaa/AccessibleWrap.h
+++ b/accessible/windows/msaa/AccessibleWrap.h
@@ -15,6 +15,7 @@
 #include "ia2AccessibleHyperlink.h"
 #include "ia2AccessibleValue.h"
 #include "mozilla/a11y/ProxyAccessible.h"
+#include "mozilla/a11y/IDSet.h"
 
 #ifdef __GNUC__
 // Inheriting from both XPCOM and MSCOM interfaces causes a lot of warnings
@@ -33,8 +34,7 @@ class AccessibleWrap : public Accessible,
                        public ia2AccessibleValue
 {
 public: // construction, destruction
-  AccessibleWrap(nsIContent* aContent, DocAccessible* aDoc) :
-    Accessible(aContent, aDoc) { }
+  AccessibleWrap(nsIContent* aContent, DocAccessible* aDoc);
 
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
@@ -152,6 +152,7 @@ public: // construction, destruction
 
   // Accessible
   virtual nsresult HandleAccEvent(AccEvent* aEvent);
+  virtual void Shutdown() override;
 
   // Helper methods
   static int32_t GetChildIDFor(Accessible* aAccessible);
@@ -176,7 +177,11 @@ public: // construction, destruction
   static IDispatch* NativeAccessible(Accessible* aAccessible);
 
 protected:
-  virtual ~AccessibleWrap() { }
+  virtual ~AccessibleWrap();
+
+#ifdef _WIN64
+  uint32_t mID;
+#endif
 
   /**
    * Creates ITypeInfo for LIBID_Accessibility if it's needed and returns it.
@@ -185,6 +190,9 @@ protected:
 
   static ITypeInfo* gTypeInfo;
 
+#ifdef _WIN64
+  static IDSet sIDGen;
+#endif
 
   enum navRelations {
     NAVRELATION_CONTROLLED_BY = 0x1000,
diff --git a/accessible/windows/msaa/DocAccessibleWrap.h b/accessible/windows/msaa/DocAccessibleWrap.h
index 80f2f41ab856..18e58b0ab3a1 100644
--- a/accessible/windows/msaa/DocAccessibleWrap.h
+++ b/accessible/windows/msaa/DocAccessibleWrap.h
@@ -34,12 +34,30 @@ public:
   // DocAccessible
   virtual void* GetNativeWindow() const;
 
+  /**
+   * Manage the mapping from id to Accessible.
+   */
+#ifdef _WIN64
+  void AddID(uint32_t aID, AccessibleWrap* aAcc)
+    { mIDToAccessibleMap.Put(aID, aAcc); }
+  void RemoveID(uint32_t aID) { mIDToAccessibleMap.Remove(aID); }
+  AccessibleWrap* GetAccessibleByID(uint32_t aID) const
+    { return mIDToAccessibleMap.Get(aID); }
+#endif
+
 protected:
   // DocAccessible
   virtual void DoInitialUpdate();
 
 protected:
   void* mHWND;
+
+  /*
+   * This provides a mapping from 32 bit id to accessible objects.
+   */
+#ifdef _WIN64
+  nsDataHashtable<nsUint32HashKey, AccessibleWrap*> mIDToAccessibleMap;
+#endif
 };
 
 } // namespace a11y