--- a/accessible/generic/Accessible.cpp
+++ b/accessible/generic/Accessible.cpp
@@ -104,17 +104,18 @@ NS_INTERFACE_MAP_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(Accessible)
 NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_DESTROY(Accessible, LastRelease())
 
 Accessible::Accessible(nsIContent* aContent, DocAccessible* aDoc) :
   mContent(aContent), mDoc(aDoc),
   mParent(nullptr), mIndexInParent(-1),
   mRoleMapEntryIndex(aria::NO_ROLE_MAP_ENTRY_INDEX),
-  mStateFlags(0), mContextFlags(0), mType(0), mGenericTypes(0)
+  mStateFlags(0), mContextFlags(0), mType(0), mGenericTypes(0),
+  mReorderEventTarget(false), mShowEventTarget(false), mHideEventTarget(false)
 {
   mBits.groupInfo = nullptr;
   mInt.mIndexOfEmbeddedChild = -1;
 }
 
 Accessible::~Accessible()
 {
   NS_ASSERTION(!mDoc, "LastRelease was never called!?!");

--- a/accessible/generic/Accessible.h
+++ b/accessible/generic/Accessible.h
@@ -951,16 +951,46 @@ public:
   bool IsARIAHidden() const { return mContextFlags & eARIAHidden; }
   void SetARIAHidden(bool aIsDefined);
 
   /**
    * Return true if the element is inside an alert.
    */
   bool IsInsideAlert() const { return mContextFlags & eInsideAlert; }
 
+  /**
+   * Return true if there is a pending reorder event for this accessible.
+   */
+  bool ReorderEventTarget() const { return mReorderEventTarget; }
+
+  /**
+   * Return true if there is a pending show event for this accessible.
+   */
+  bool ShowEventTarget() const { return mShowEventTarget; }
+
+  /**
+   * Return true if there is a pending hide event for this accessible.
+   */
+  bool HideEventTarget() const { return mHideEventTarget; }
+
+  /**
+   * Set if there is a pending reorder event for this accessible.
+   */
+  void SetReorderEventTarget(bool aTarget) { mReorderEventTarget = aTarget; }
+
+  /**
+   * Set if this accessible is a show event target.
+   */
+  void SetShowEventTarget(bool aTarget) { mShowEventTarget = aTarget; }
+
+  /**
+   * Set if this accessible is a hide event target.
+   */
+  void SetHideEventTarget(bool aTarget) { mHideEventTarget = aTarget; }
+
 protected:
   virtual ~Accessible();
 
   /**
    * Return the accessible name provided by native markup. It doesn't take
    * into account ARIA markup used to specify the name.
    */
   virtual mozilla::a11y::ENameValueFlag NativeName(nsString& aName);
@@ -1127,16 +1157,19 @@ protected:
 
   /**
    * Keep in sync with StateFlags, ContextFlags, and AccTypes.
    */
   uint32_t mStateFlags : kStateFlagsBits;
   uint32_t mContextFlags : kContextFlagsBits;
   uint32_t mType : kTypeBits;
   uint32_t mGenericTypes : kGenericTypesBits;
+  uint32_t mReorderEventTarget : 1;
+  uint32_t mShowEventTarget : 1;
+  uint32_t mHideEventTarget : 1;
 
   void StaticAsserts() const;
 
 #ifdef A11Y_LOG
   friend void logging::Tree(const char* aTitle, const char* aMsgText,
                             Accessible* aRoot,
                             logging::GetTreePrefix aPrefixFunc,
                             void* aGetTreePrefixData);