diff --git a/source/virtualBuffers/gecko_ia2.py b/source/virtualBuffers/gecko_ia2.py
index 20072036c4e..f8b4003ca98 100755
--- a/source/virtualBuffers/gecko_ia2.py
+++ b/source/virtualBuffers/gecko_ia2.py
@@ -2,7 +2,7 @@
 #A part of NonVisual Desktop Access (NVDA)
 #This file is covered by the GNU General Public License.
 #See the file COPYING for more details.
-#Copyright (C) 2008-2017 NV Access Limited, Babbage B.V.
+#Copyright (C) 2008-2017 NV Access Limited, Babbage B.V., Mozilla Corporation
 
 from . import VirtualBuffer, VirtualBufferTextInfo, VBufStorage_findMatch_word, VBufStorage_findMatch_notEmpty
 import treeInterceptorHandler
@@ -99,14 +99,29 @@ def _get_shouldPrepare(self):
 			return False
 		return True
 
+	def _getExpandedComboBox(self, obj):
+		"""If obj is an item in an expanded combo box, get the combo box.
+		"""
+		if not (obj.windowClassName.startswith('Mozilla') and obj.windowStyle & winUser.WS_POPUP):
+			# This is not a Mozilla popup window, so it can't be an expanded combo box.
+			return None
+		if obj.role not in (controlTypes.ROLE_LISTITEM, controlTypes.ROLE_LIST):
+			return None
+		parent = obj.parent
+		# Try a maximum of 2 ancestors, since we might be on the list item or the list.
+		for i in xrange(2):
+			obj = obj.parent
+			if not obj:
+				return None
+			if obj.role == controlTypes.ROLE_COMBOBOX:
+				return obj
+		return None
+
 	def __contains__(self,obj):
-		#Special code to handle Mozilla combobox lists
-		if obj.windowClassName.startswith('Mozilla') and winUser.getWindowStyle(obj.windowHandle)&winUser.WS_POPUP:
-			parent=obj.parent
-			while parent and parent.windowHandle==obj.windowHandle:
-				parent=parent.parent
-			if parent:
-				obj=parent.parent
+		# if this is a Mozilla combo box popup, we want to work with the combo box.
+		combo = self._getExpandedComboBox(obj)
+		if combo:
+			obj = combo
 		if not (isinstance(obj,NVDAObjects.IAccessible.IAccessible) and isinstance(obj.IAccessibleObject,IAccessibleHandler.IAccessible2)) or not obj.windowClassName.startswith('Mozilla') or not winUser.isDescendantWindow(self.rootNVDAObject.windowHandle,obj.windowHandle):
 			return False
 		if self.rootNVDAObject.windowHandle==obj.windowHandle: