--- a/accessible/atk/AccessibleWrap.cpp
+++ b/accessible/atk/AccessibleWrap.cpp
@@ -850,16 +850,23 @@ refChildCB(AtkObject *aAtkObj, gint aChi
   return childAtkObj;
 }
 
 gint
 getIndexInParentCB(AtkObject* aAtkObj)
 {
   // We don't use Accessible::IndexInParent() because we don't include text
   // leaf nodes as children in ATK.
+  if (ProxyAccessible* proxy = GetProxy(aAtkObj)) {
+    if (ProxyAccessible* parent = proxy->Parent())
+      return parent->IndexOfEmbeddedChild(proxy);
+
+    return -1;
+  }
+
     AccessibleWrap* accWrap = GetAccessibleWrap(aAtkObj);
     if (!accWrap) {
         return -1;
     }
 
     Accessible* parent = accWrap->Parent();
     if (!parent)
         return -1; // No parent

--- a/accessible/ipc/DocAccessibleChild.cpp
+++ b/accessible/ipc/DocAccessibleChild.cpp
@@ -1614,16 +1614,32 @@ DocAccessibleChild::RecvTakeFocus(const 
   if (acc) {
     acc->TakeFocus();
   }
 
   return true;
 }
 
 bool
+DocAccessibleChild::RecvIndexOfEmbeddedChild(const uint64_t& aID,
+                                             const uint64_t& aChildID,
+                                             uint32_t* aChildIdx)
+{
+  *aChildIdx = 0;
+
+  Accessible* parent = IdToAccessible(aID);
+  Accessible* child = IdToAccessible(aChildID);
+  if (!parent || !child)
+    return true;
+
+  *aChildIdx = parent->GetIndexOfEmbeddedChild(child);
+  return true;
+}
+
+bool
 DocAccessibleChild::RecvChildAtPoint(const uint64_t& aID,
                                      const int32_t& aX,
                                      const int32_t& aY,
                                      const uint32_t& aWhich,
                                      uint64_t* aChild,
                                      bool* aOk)
 {
   *aChild = 0;

--- a/accessible/ipc/DocAccessibleChild.h
+++ b/accessible/ipc/DocAccessibleChild.h
@@ -388,16 +388,20 @@ public:
   virtual bool RecvMaxValue(const uint64_t& aID,
                             double* aValue) override;
 
   virtual bool RecvStep(const uint64_t& aID,
                         double* aStep) override;
 
   virtual bool RecvTakeFocus(const uint64_t& aID) override;
 
+  virtual bool RecvIndexOfEmbeddedChild(const uint64_t& aID,
+                                        const uint64_t& aChildID,
+                                        uint32_t* aChildIdx) override final;
+
   virtual bool RecvChildAtPoint(const uint64_t& aID,
                                 const int32_t& aX,
                                 const int32_t& aY,
                                 const uint32_t& aWhich,
                                 uint64_t* aChild,
                                 bool* aOk) override;
 
   virtual bool RecvBounds(const uint64_t& aID, nsIntRect* aRect) override;

--- a/accessible/ipc/PDocAccessible.ipdl
+++ b/accessible/ipc/PDocAccessible.ipdl
@@ -206,16 +206,18 @@ child:
 
   prio(high) sync CurValue(uint64_t aID) returns(double aValue);
   prio(high) sync SetCurValue(uint64_t aID, double aValue) returns(bool aRetVal);
   prio(high) sync MinValue(uint64_t aID) returns(double aValue);
   prio(high) sync MaxValue(uint64_t aID) returns(double aValue);
   prio(high) sync Step(uint64_t aID) returns(double aStep);
 
   prio(high) sync TakeFocus(uint64_t aID);
+  prio(high) sync IndexOfEmbeddedChild(uint64_t aID, uint64_t aChildID)
+    returns(uint32_t childIdx);
   prio(high) sync ChildAtPoint(uint64_t aID, int32_t aX, int32_t aY, uint32_t aWhich)
     returns(uint64_t aChild, bool aOk);
   prio(high) sync Bounds(uint64_t aID) returns(nsIntRect aRect);
 
   prio(high) sync Language(uint64_t aID) returns(nsString aLocale);
   prio(high) sync DocType(uint64_t aID) returns(nsString aType);
   prio(high) sync URL(uint64_t aID) returns(nsString aURL);
   prio(high) sync MimeType(uint64_t aID) returns(nsString aMime);

--- a/accessible/ipc/ProxyAccessible.cpp
+++ b/accessible/ipc/ProxyAccessible.cpp
@@ -898,16 +898,25 @@ ProxyAccessible::Step()
 }
 
 void
 ProxyAccessible::TakeFocus()
 {
   unused << mDoc->SendTakeFocus(mID);
 }
 
+int32_t
+ProxyAccessible::IndexOfEmbeddedChild(const ProxyAccessible* aChild)
+{
+  uint64_t childID = aChild->mID;
+  uint32_t childIdx;
+  unused << mDoc->SendIndexOfEmbeddedChild(mID, childID, &childIdx);
+  return childIdx;
+}
+
 ProxyAccessible*
 ProxyAccessible::ChildAtPoint(int32_t aX, int32_t aY,
                               Accessible::EWhichChildAtPoint aWhichChild)
 {
   uint64_t childID = 0;
   bool ok = false;
   unused << mDoc->SendChildAtPoint(mID, aX, aY,
                                    static_cast<uint32_t>(aWhichChild),

--- a/accessible/ipc/ProxyAccessible.h
+++ b/accessible/ipc/ProxyAccessible.h
@@ -42,16 +42,17 @@ public:
   void AddChildAt(uint32_t aIdx, ProxyAccessible* aChild)
   { mChildren.InsertElementAt(aIdx, aChild); }
 
   uint32_t ChildrenCount() const { return mChildren.Length(); }
   ProxyAccessible* ChildAt(uint32_t aIdx) const { return mChildren[aIdx]; }
 
   // XXX evaluate if this is fast enough.
   size_t IndexInParent() const { return mParent->mChildren.IndexOf(this); }
+  int32_t IndexOfEmbeddedChild(const ProxyAccessible*);
   bool MustPruneChildren() const;
 
   void Shutdown();
 
   void SetChildDoc(DocAccessibleParent*);
 
   /**
    * Remove The given child.