diff --git a/content/base/public/nsIContent.h b/content/base/public/nsIContent.h
index 105be819376..8dae699bbb7 100644
--- a/content/base/public/nsIContent.h
+++ b/content/base/public/nsIContent.h
@@ -63,8 +63,8 @@ class nsIDocShell;
 
 // IID for the nsIContent interface
 #define NS_ICONTENT_IID       \
-{ 0x36b375cb, 0xf01e, 0x4c18, \
-  { 0xbf, 0x9e, 0xba, 0xad, 0x77, 0x1d, 0xce, 0x22 } }
+{ 0x609baee8, 0x3c0a, 0x4122, \
+  { 0x9c, 0xc6, 0xe4, 0xc9, 0x83, 0x53, 0xff, 0x9c } }
 
 // hack to make egcs / gcc 2.95.2 happy
 class nsIContent_base : public nsINode {
@@ -211,10 +211,21 @@ public:
 
   /**
    * Returns an atom holding the name of the attribute of type ID on
-   * this content node (if applicable).  Returns null for non-element
-   * content nodes.
+   * this content node (if applicable).
+   * Language specific ID attribute has the highest priority, then
+   * ID attribute defined in DTD, and finally xml:id.
+   * Returns null for non-element content nodes.
    */
-  virtual nsIAtom *GetIDAttributeName() const = 0;
+  virtual nsIAtom* GetIDAttributeName(PRInt32& aNameSpaceID) const = 0;
+
+  /**
+   * Returns true if the attribute can be
+   * used as an ID attribute of the element.
+   * Note this may return true with many attributes, but only one
+   * is used as an ID at a time.
+   */
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const = 0;
 
   /**
    * Normalizes an attribute name and returns it as a nodeinfo if an attribute
@@ -731,8 +742,8 @@ public:
 
   /**
    * Get the ID of this content node (the atom corresponding to the
-   * value of the null-namespace attribute whose name is given by
-   * GetIDAttributeName().  This may be null if there is no ID.
+   * value of the attribute whose name is given by GetIDAttributeName().
+   * This may be null if there is no ID.
    */
   virtual nsIAtom* GetID() const = 0;
 
diff --git a/content/base/src/nsDOMAttribute.cpp b/content/base/src/nsDOMAttribute.cpp
index d01023df035..fd31bbfbe09 100644
--- a/content/base/src/nsDOMAttribute.cpp
+++ b/content/base/src/nsDOMAttribute.cpp
@@ -600,14 +600,15 @@ nsDOMAttribute::GetIsId(PRBool* aReturn)
     return NS_OK;
   }
 
-  nsIAtom* idAtom = content->GetIDAttributeName();
+  PRInt32 namespaceID;
+  nsIAtom* idAtom = content->GetIDAttributeName(namespaceID);
   if (!idAtom)
   {
     *aReturn = PR_FALSE;
     return NS_OK;
   }
 
-  *aReturn = mNodeInfo->Equals(idAtom, kNameSpaceID_None);
+  *aReturn = mNodeInfo->Equals(idAtom, namespaceID);
   return NS_OK;
 }
 
diff --git a/content/base/src/nsGenericDOMDataNode.cpp b/content/base/src/nsGenericDOMDataNode.cpp
index 5f436eae71b..4ea0c2bd2e7 100644
--- a/content/base/src/nsGenericDOMDataNode.cpp
+++ b/content/base/src/nsGenericDOMDataNode.cpp
@@ -631,11 +631,19 @@ nsGenericDOMDataNode::UnbindFromTree(PRBool aDeep, PRBool aNullParent)
 }
 
 nsIAtom *
-nsGenericDOMDataNode::GetIDAttributeName() const
+nsGenericDOMDataNode::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
+  aNameSpaceID = kNameSpaceID_Unknown;
   return nsnull;
 }
 
+PRBool
+nsGenericDOMDataNode::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                                 nsIAtom* aAtom) const
+{
+  return PR_FALSE;
+}
+
 already_AddRefed<nsINodeInfo>
 nsGenericDOMDataNode::GetExistingAttrNameFromQName(const nsAString& aStr) const
 {
diff --git a/content/base/src/nsGenericDOMDataNode.h b/content/base/src/nsGenericDOMDataNode.h
index dedcbcd51c9..e076d48b1ed 100644
--- a/content/base/src/nsGenericDOMDataNode.h
+++ b/content/base/src/nsGenericDOMDataNode.h
@@ -195,7 +195,9 @@ public:
   virtual void UnbindFromTree(PRBool aDeep = PR_TRUE,
                               PRBool aNullParent = PR_TRUE);
 
-  virtual nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNamespaceId) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   virtual already_AddRefed<nsINodeInfo> GetExistingAttrNameFromQName(const nsAString& aStr) const;
   nsresult SetAttr(PRInt32 aNameSpaceID, nsIAtom* aName,
                    const nsAString& aValue, PRBool aNotify)
diff --git a/content/base/src/nsGenericElement.cpp b/content/base/src/nsGenericElement.cpp
index 92044c5a8df..d6b8b9f3d4c 100644
--- a/content/base/src/nsGenericElement.cpp
+++ b/content/base/src/nsGenericElement.cpp
@@ -2260,9 +2260,10 @@ nsGenericElement::DispatchDOMEvent(nsEvent* aEvent,
 nsIAtom*
 nsGenericElement::GetID() const
 {
-  nsIAtom* IDName = GetIDAttributeName();
+  PRInt32 namespaceID;
+  nsIAtom* IDName = GetIDAttributeName(namespaceID);
   if (IDName) {
-    const nsAttrValue* attrVal = mAttrsAndChildren.GetAttr(IDName);
+    const nsAttrValue* attrVal = mAttrsAndChildren.GetAttr(IDName, namespaceID);
     if (attrVal){
       if (attrVal->Type() == nsAttrValue::eAtom) {
         return attrVal->GetAtomValue();
@@ -2325,9 +2326,26 @@ nsGenericElement::GetAttributeChangeHint(const nsIAtom* aAttribute,
 }
 
 nsIAtom *
-nsGenericElement::GetIDAttributeName() const
+nsGenericElement::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
-  return mNodeInfo->GetIDAttributeAtom();
+  aNameSpaceID = kNameSpaceID_None;
+  nsIAtom* idAtom = mNodeInfo->GetIDAttributeAtom();
+  if (idAtom && HasAttr(aNameSpaceID, idAtom)) {
+    return idAtom;
+  }
+
+  aNameSpaceID = kNameSpaceID_XML;
+  return nsGkAtoms::id;
+}
+
+PRBool
+nsGenericElement::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                             nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None &&
+          aAtom == mNodeInfo->GetIDAttributeAtom()) ||
+         (aNameSpaceID == kNameSpaceID_XML &&
+          aAtom == nsGkAtoms::id);
 }
 
 nsIAtom *
@@ -3652,8 +3670,8 @@ nsGenericElement::ParseAttribute(PRInt32 aNamespaceID,
                                  const nsAString& aValue,
                                  nsAttrValue& aResult)
 {
-  if (aNamespaceID == kNameSpaceID_None &&
-      aAttribute == GetIDAttributeName() && !aValue.IsEmpty()) {
+  if (IsPotentialIDAttributeName(aNamespaceID, aAttribute) &&
+      !aValue.IsEmpty()) {
     // Store id as an atom.  id="" means that the element has no id,
     // not that it has an emptystring as the id.
     aResult.ParseAtom(aValue);
diff --git a/content/base/src/nsGenericElement.h b/content/base/src/nsGenericElement.h
index 3b8c9b835d5..61bfea5e020 100644
--- a/content/base/src/nsGenericElement.h
+++ b/content/base/src/nsGenericElement.h
@@ -383,7 +383,9 @@ public:
                               PRBool aCompileEventHandlers);
   virtual void UnbindFromTree(PRBool aDeep = PR_TRUE,
                               PRBool aNullParent = PR_TRUE);
-  virtual nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   virtual nsIAtom *GetClassAttributeName() const;
   virtual already_AddRefed<nsINodeInfo> GetExistingAttrNameFromQName(const nsAString& aStr) const;
   nsresult SetAttr(PRInt32 aNameSpaceID, nsIAtom* aName,
diff --git a/content/events/src/nsXMLEventsElement.cpp b/content/events/src/nsXMLEventsElement.cpp
index 37c07a419d7..4c850345913 100644
--- a/content/events/src/nsXMLEventsElement.cpp
+++ b/content/events/src/nsXMLEventsElement.cpp
@@ -46,7 +46,9 @@ public:
   virtual ~nsXMLEventsElement();
   NS_FORWARD_NSIDOMNODE(nsXMLElement::)
 
-  virtual nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   virtual nsresult SetAttr(PRInt32 aNameSpaceID, nsIAtom* aName, 
                            nsIAtom* aPrefix, const nsAString& aValue,
                            PRBool aNotify);
@@ -63,11 +65,21 @@ nsXMLEventsElement::~nsXMLEventsElement()
 }
 
 nsIAtom *
-nsXMLEventsElement::GetIDAttributeName() const
+nsXMLEventsElement::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
-  if (mNodeInfo->Equals(nsGkAtoms::listener))
+  if (HasAttr(kNameSpaceID_None, nsGkAtoms::id)) {
+    aNameSpaceID = kNameSpaceID_None;
     return nsGkAtoms::id;
-  return nsXMLElement::GetIDAttributeName();
+  }
+  return nsGenericElement::GetIDAttributeName(aNameSpaceID);
+}
+
+PRBool
+nsXMLEventsElement::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                               nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None && aAtom == nsGkAtoms::id) ||
+    nsGenericElement::IsPotentialIDAttributeName(aNameSpaceID, aAtom);
 }
 
 nsresult
diff --git a/content/events/src/nsXMLEventsManager.cpp b/content/events/src/nsXMLEventsManager.cpp
index 0924f30b2a3..f17cbcd1109 100644
--- a/content/events/src/nsXMLEventsManager.cpp
+++ b/content/events/src/nsXMLEventsManager.cpp
@@ -377,20 +377,11 @@ nsXMLEventsManager::AttributeChanged(nsIDocument* aDocument,
       AddXMLEventsContent(aContent);
       nsXMLEventsListener::InitXMLEventsListener(aDocument, this, aContent);
     }
-    else if (aContent->GetIDAttributeName() == aAttribute) {
-      if (aModType == nsIDOMMutationEvent::REMOVAL)
-        mListeners.Enumerate(EnumAndSetIncomplete, aContent);
-      else if (aModType == nsIDOMMutationEvent::MODIFICATION) {
-        //Remove possible listener
-        mListeners.Enumerate(EnumAndSetIncomplete, aContent);
-        //Add new listeners
-        AddListeners(aDocument);
-      }
-      else {
-        //If we are adding the ID attribute, we must check whether we can 
-        //add new listeners
-        AddListeners(aDocument);
-      }
+    else if (aContent->IsPotentialIDAttributeName(aNameSpaceID, aAttribute)) {
+      //Remove possible listener
+      mListeners.Enumerate(EnumAndSetIncomplete, aContent);
+      //Add new listeners
+      AddListeners(aDocument);
     }
   }
 }
diff --git a/content/html/content/src/nsGenericHTMLElement.cpp b/content/html/content/src/nsGenericHTMLElement.cpp
index 63ff13081bb..f0eebb8fb77 100644
--- a/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/content/html/content/src/nsGenericHTMLElement.cpp
@@ -1493,9 +1493,21 @@ nsGenericHTMLElement::GetClasses() const
 }
 
 nsIAtom *
-nsGenericHTMLElement::GetIDAttributeName() const
+nsGenericHTMLElement::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
-  return nsGkAtoms::id;
+  if (HasAttr(kNameSpaceID_None, nsGkAtoms::id)) {
+    aNameSpaceID = kNameSpaceID_None;
+    return nsGkAtoms::id;
+  }
+  return nsGenericElement::GetIDAttributeName(aNameSpaceID);
+}
+
+PRBool
+nsGenericHTMLElement::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                                 nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None && aAtom == nsGkAtoms::id) ||
+    nsGenericElement::IsPotentialIDAttributeName(aNameSpaceID, aAtom);
 }
 
 nsIAtom *
diff --git a/content/html/content/src/nsGenericHTMLElement.h b/content/html/content/src/nsGenericHTMLElement.h
index 8a6c0cb8f91..63d05800cb1 100644
--- a/content/html/content/src/nsGenericHTMLElement.h
+++ b/content/html/content/src/nsGenericHTMLElement.h
@@ -241,7 +241,9 @@ public:
   virtual void UpdateEditableState();
 
   virtual const nsAttrValue* GetClasses() const;
-  virtual nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   virtual nsIAtom *GetClassAttributeName() const;
   NS_IMETHOD WalkContentStyleRules(nsRuleWalker* aRuleWalker);
   virtual nsICSSStyleRule* GetInlineStyleRule();
diff --git a/content/html/document/src/nsHTMLDocument.cpp b/content/html/document/src/nsHTMLDocument.cpp
index 032b30f2f3c..6dc67af4c6d 100644
--- a/content/html/document/src/nsHTMLDocument.cpp
+++ b/content/html/document/src/nsHTMLDocument.cpp
@@ -1376,8 +1376,7 @@ nsHTMLDocument::AttributeWillChange(nsIContent* aContent, PRInt32 aNameSpaceID,
         return;
       }
     }
-  } else if (aAttribute == aContent->GetIDAttributeName() &&
-             aNameSpaceID == kNameSpaceID_None) {
+  } else if (aContent->IsPotentialIDAttributeName(aNameSpaceID, aAttribute)) {
     nsresult rv = RemoveFromIdTable(aContent);
 
     if (NS_FAILED(rv)) {
@@ -1406,8 +1405,7 @@ nsHTMLDocument::AttributeChanged(nsIDocument* aDocument,
     if (name) {
       UpdateNameTableEntry(name, aContent);
     }
-  } else if (aAttribute == aContent->GetIDAttributeName() &&
-             aNameSpaceID == kNameSpaceID_None) {
+  } else if (aContent->IsPotentialIDAttributeName(aNameSpaceID, aAttribute)) {
     nsIAtom* id = aContent->GetID();
     if (id) {
       UpdateIdTableEntry(id, aContent);
diff --git a/content/svg/content/src/nsSVGElement.cpp b/content/svg/content/src/nsSVGElement.cpp
index 247f376d4bc..1fcca6bc4b8 100644
--- a/content/svg/content/src/nsSVGElement.cpp
+++ b/content/svg/content/src/nsSVGElement.cpp
@@ -126,10 +126,22 @@ NS_INTERFACE_MAP_END_INHERITING(nsGenericElement)
 //----------------------------------------------------------------------
 // nsIContent methods
 
-nsIAtom *
-nsSVGElement::GetIDAttributeName() const
+nsIAtom*
+nsSVGElement::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
-  return nsGkAtoms::id;
+  if (HasAttr(kNameSpaceID_None, nsGkAtoms::id)) {
+    aNameSpaceID = kNameSpaceID_None;
+    return nsGkAtoms::id;
+  }
+  return nsGenericElement::GetIDAttributeName(aNameSpaceID);
+}
+
+PRBool
+nsSVGElement::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                         nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None && aAtom == nsGkAtoms::id) ||
+    nsGenericElement::IsPotentialIDAttributeName(aNameSpaceID, aAtom);
 }
 
 nsIAtom *
diff --git a/content/svg/content/src/nsSVGElement.h b/content/svg/content/src/nsSVGElement.h
index c7c31416867..9db34f2f55c 100644
--- a/content/svg/content/src/nsSVGElement.h
+++ b/content/svg/content/src/nsSVGElement.h
@@ -71,7 +71,9 @@ public:
 
   // nsIContent interface methods
 
-  virtual nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   virtual nsIAtom *GetClassAttributeName() const;
   virtual nsresult UnsetAttr(PRInt32 aNameSpaceID, nsIAtom* aAttribute,
                              PRBool aNotify);
diff --git a/content/xtf/src/nsXTFElementWrapper.cpp b/content/xtf/src/nsXTFElementWrapper.cpp
index 9fdeb951713..638d7d8f8d8 100644
--- a/content/xtf/src/nsXTFElementWrapper.cpp
+++ b/content/xtf/src/nsXTFElementWrapper.cpp
@@ -265,10 +265,21 @@ nsXTFElementWrapper::RemoveChildAt(PRUint32 aIndex, PRBool aNotify)
 }
 
 nsIAtom *
-nsXTFElementWrapper::GetIDAttributeName() const
+nsXTFElementWrapper::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
-  // XXX:
-  return nsGkAtoms::id;
+  if (HasAttr(kNameSpaceID_None, nsGkAtoms::id)) {
+    aNameSpaceID = kNameSpaceID_None;
+    return nsGkAtoms::id;
+  }
+  return nsXTFElementWrapperBase::GetIDAttributeName(aNameSpaceID);
+}
+
+PRBool
+nsXTFElementWrapper::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                                nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None && aAtom == nsGkAtoms::id) ||
+    nsXTFElementWrapperBase::IsPotentialIDAttributeName(aNameSpaceID, aAtom);
 }
 
 nsresult
diff --git a/content/xtf/src/nsXTFElementWrapper.h b/content/xtf/src/nsXTFElementWrapper.h
index b85fae77736..3001ffcc2b1 100644
--- a/content/xtf/src/nsXTFElementWrapper.h
+++ b/content/xtf/src/nsXTFElementWrapper.h
@@ -78,7 +78,9 @@ public:
   nsresult InsertChildAt(nsIContent* aKid, PRUint32 aIndex,
                          PRBool aNotify);
   nsresult RemoveChildAt(PRUint32 aIndex, PRBool aNotify);
-  nsIAtom *GetIDAttributeName() const;
+  virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+  virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                            nsIAtom* aAtom) const;
   nsresult SetAttr(PRInt32 aNameSpaceID, nsIAtom* aName,
                    nsIAtom* aPrefix, const nsAString& aValue,
                    PRBool aNotify);
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index 770477b2532..5f3e842a80a 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -1633,7 +1633,9 @@ nsXULElement::InsertChildAt(nsIContent* aKid, PRUint32 aIndex, PRBool aNotify)
 nsIAtom*
 nsXULElement::GetID() const
 {
-    const nsAttrValue* attrVal = FindLocalOrProtoAttr(kNameSpaceID_None, nsGkAtoms::id);
+    PRInt32 namespaceID;
+    nsIAtom* IDName = GetIDAttributeName(namespaceID);
+    const nsAttrValue* attrVal = FindLocalOrProtoAttr(namespaceID, IDName);
 
     NS_ASSERTION(!attrVal ||
                  attrVal->Type() == nsAttrValue::eAtom ||
@@ -1739,9 +1741,21 @@ nsXULElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 }
 
 nsIAtom *
-nsXULElement::GetIDAttributeName() const
+nsXULElement::GetIDAttributeName(PRInt32& aNameSpaceID) const
 {
+  if (HasAttr(kNameSpaceID_None, nsGkAtoms::id)) {
+    aNameSpaceID = kNameSpaceID_None;
     return nsGkAtoms::id;
+  }
+  return nsGenericElement::GetIDAttributeName(aNameSpaceID);
+}
+
+PRBool
+nsXULElement::IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                         nsIAtom* aAtom) const
+{
+  return (aNameSpaceID == kNameSpaceID_None && aAtom == nsGkAtoms::id) ||
+    nsGenericElement::IsPotentialIDAttributeName(aNameSpaceID, aAtom);
 }
 
 nsIAtom *
diff --git a/content/xul/content/src/nsXULElement.h b/content/xul/content/src/nsXULElement.h
index 3da3a6dea12..75193ac4eff 100644
--- a/content/xul/content/src/nsXULElement.h
+++ b/content/xul/content/src/nsXULElement.h
@@ -505,7 +505,9 @@ public:
     virtual void UnbindFromTree(PRBool aDeep, PRBool aNullParent);
     virtual void SetNativeAnonymous(PRBool aAnonymous);
     virtual nsresult RemoveChildAt(PRUint32 aIndex, PRBool aNotify);
-    virtual nsIAtom *GetIDAttributeName() const;
+    virtual nsIAtom *GetIDAttributeName(PRInt32& aNameSpaceID) const;
+    virtual PRBool IsPotentialIDAttributeName(PRInt32 aNameSpaceID,
+                                              nsIAtom* aAtom) const;
     virtual nsIAtom *GetClassAttributeName() const;
     virtual PRBool GetAttr(PRInt32 aNameSpaceID, nsIAtom* aName,
                            nsAString& aResult) const;
diff --git a/content/xul/document/src/nsXULDocument.cpp b/content/xul/document/src/nsXULDocument.cpp
index 88de793d1e4..5f422e1fc23 100644
--- a/content/xul/document/src/nsXULDocument.cpp
+++ b/content/xul/document/src/nsXULDocument.cpp
@@ -929,7 +929,8 @@ nsXULDocument::AttributeChanged(nsIDocument* aDocument,
 
     // XXXbz check aNameSpaceID, dammit!
     // First see if we need to update our element map.
-    if ((aAttribute == nsGkAtoms::id) || (aAttribute == nsGkAtoms::ref)) {
+    if (aElement->IsPotentialIDAttributeName(aNameSpaceID, aAttribute) ||
+        (aAttribute == nsGkAtoms::ref && aNameSpaceID == kNameSpaceID_None)) {
 
         rv = mElementMap.Enumerate(RemoveElementsFromMapByContent, aElement);
         if (NS_FAILED(rv)) return;
@@ -1757,31 +1758,29 @@ nsXULDocument::GetTemplateBuilderFor(nsIContent* aContent,
     return NS_OK;
 }
 
-// Attributes that are used with getElementById() and the
-// resource-to-element map.
-nsIAtom** nsXULDocument::kIdentityAttrs[] =
-{
-    &nsGkAtoms::id,
-    &nsGkAtoms::ref,
-    nsnull
-};
-
 nsresult
 nsXULDocument::AddElementToMap(nsIContent* aElement)
 {
-    // Look at the element's 'id' and 'ref' attributes, and if set,
+    // Look at the element's ID and 'ref' attributes, and if set,
     // add pointers in the resource-to-element map to the element.
     nsresult rv;
-
-    for (PRInt32 i = 0; kIdentityAttrs[i] != nsnull; ++i) {
-        nsAutoString value;
-        aElement->GetAttr(kNameSpaceID_None, *kIdentityAttrs[i], value);
-        if (!value.IsEmpty()) {
-            rv = mElementMap.Add(value, aElement);
-            if (NS_FAILED(rv)) return rv;
+    nsIAtom* idAtom = aElement->GetID();
+    if (idAtom) {
+        nsAutoString idStr;
+        idAtom->ToString(idStr);
+        if (!idStr.IsEmpty()) {
+            rv = mElementMap.Add(idStr, aElement);
+            NS_ENSURE_SUCCESS(rv, rv);
         }
     }
 
+    nsAutoString refvalue;
+    aElement->GetAttr(kNameSpaceID_None, nsGkAtoms::ref, refvalue);
+    if (!refvalue.IsEmpty()) {
+        rv = mElementMap.Add(refvalue, aElement);
+        NS_ENSURE_SUCCESS(rv, rv);
+    }
+
     return NS_OK;
 }
 
@@ -1791,16 +1790,23 @@ nsXULDocument::RemoveElementFromMap(nsIContent* aElement)
 {
     // Remove the element from the resource-to-element map.
     nsresult rv;
-
-    for (PRInt32 i = 0; kIdentityAttrs[i] != nsnull; ++i) {
-        nsAutoString value;
-        aElement->GetAttr(kNameSpaceID_None, *kIdentityAttrs[i], value);
-        if (!value.IsEmpty()) {
-            rv = mElementMap.Remove(value, aElement);
-            if (NS_FAILED(rv)) return rv;
+    nsIAtom* idAtom = aElement->GetID();
+    if (idAtom) {
+        nsAutoString idStr;
+        idAtom->ToString(idStr);
+        if (!idStr.IsEmpty()) {
+            rv = mElementMap.Remove(idStr, aElement);
+            NS_ENSURE_SUCCESS(rv, rv);
         }
     }
 
+    nsAutoString refvalue;
+    aElement->GetAttr(kNameSpaceID_None, nsGkAtoms::ref, refvalue);
+    if (!refvalue.IsEmpty()) {
+        rv = mElementMap.Remove(refvalue, aElement);
+        NS_ENSURE_SUCCESS(rv, rv);
+    }
+
     return NS_OK;
 }
 
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index e65a9ab2bcf..e5f18c4e0f2 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -10128,7 +10128,8 @@ nsCSSFrameConstructor::AttributeChanged(nsIContent* aContent,
 #endif
 
   // the style tag has its own interpretation based on aHint 
-  nsChangeHint hint = aContent->GetAttributeChangeHint(aAttribute, aModType);
+  nsChangeHint hint = (aNameSpaceID == kNameSpaceID_None)
+    ? aContent->GetAttributeChangeHint(aAttribute, aModType) : nsChangeHint(0);
 
   PRBool reframe = (hint & nsChangeHint_ReconstructFrame) != 0;
 
@@ -10163,15 +10164,19 @@ nsCSSFrameConstructor::AttributeChanged(nsIContent* aContent,
 
   if (primaryFrame) {
     // See if we have appearance information for a theme.
-    const nsStyleDisplay* disp = primaryFrame->GetStyleDisplay();
-    if (disp->mAppearance) {
-      nsPresContext* presContext = mPresShell->GetPresContext();
-      nsITheme *theme = presContext->GetTheme();
-      if (theme && theme->ThemeSupportsWidget(presContext, primaryFrame, disp->mAppearance)) {
-        PRBool repaint = PR_FALSE;
-        theme->WidgetStateChanged(primaryFrame, disp->mAppearance, aAttribute, &repaint);
-        if (repaint)
-          NS_UpdateHint(hint, nsChangeHint_RepaintFrame);
+    if (aNameSpaceID == kNameSpaceID_None) {
+      const nsStyleDisplay* disp = primaryFrame->GetStyleDisplay();
+      if (disp->mAppearance) {
+        nsPresContext* presContext = mPresShell->GetPresContext();
+        nsITheme *theme = presContext->GetTheme();
+        if (theme && theme->ThemeSupportsWidget(presContext, primaryFrame,
+                                                disp->mAppearance)) {
+          PRBool repaint = PR_FALSE;
+          theme->WidgetStateChanged(primaryFrame, disp->mAppearance, aAttribute,
+                                    &repaint);
+          if (repaint)
+            NS_UpdateHint(hint, nsChangeHint_RepaintFrame);
+        }
       }
     }
    
@@ -10188,6 +10193,7 @@ nsCSSFrameConstructor::AttributeChanged(nsIContent* aContent,
   // the frame's AttributeChanged() in case it does something that affects the style
   nsFrameManager *frameManager = shell->FrameManager();
   nsReStyleHint rshint = frameManager->HasAttributeDependentStyle(aContent,
+                                                                  aNameSpaceID,
                                                                   aAttribute,
                                                                   aModType,
                                                                   aStateMask);
diff --git a/layout/base/nsFrameManager.cpp b/layout/base/nsFrameManager.cpp
index c1e0a2e870a..76fcd07c996 100644
--- a/layout/base/nsFrameManager.cpp
+++ b/layout/base/nsFrameManager.cpp
@@ -1445,12 +1445,14 @@ nsFrameManager::ComputeStyleChangeFor(nsIFrame          *aFrame,
 
 nsReStyleHint
 nsFrameManager::HasAttributeDependentStyle(nsIContent *aContent,
+                                           PRInt32 aNameSpaceID,
                                            nsIAtom *aAttribute,
                                            PRInt32 aModType,
                                            PRUint32 aStateMask)
 {
   nsReStyleHint hint = mStyleSet->HasAttributeDependentStyle(GetPresContext(),
                                                              aContent,
+                                                             aNameSpaceID,
                                                              aAttribute,
                                                              aModType,
                                                              aStateMask);
diff --git a/layout/base/nsFrameManager.h b/layout/base/nsFrameManager.h
index 31cd2cc2688..556d4c6e8ec 100644
--- a/layout/base/nsFrameManager.h
+++ b/layout/base/nsFrameManager.h
@@ -191,6 +191,7 @@ public:
 
   // Determine whether an attribute affects style
   NS_HIDDEN_(nsReStyleHint) HasAttributeDependentStyle(nsIContent *aContent,
+                                                       PRInt32 aNameSpaceID,
                                                        nsIAtom *aAttribute,
                                                        PRInt32 aModType,
                                                        PRUint32 aStateMask);
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index fe360c931f7..15cb92d4115 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -1001,6 +1001,8 @@ static PRBool AttrMatchesValue(const nsAttrSelector* aAttrSelector,
 static PRBool SelectorMatches(RuleProcessorData &data,
                               nsCSSSelector* aSelector,
                               PRInt32 aStateMask, // states NOT to test
+                              PRInt32 aNameSpaceID, // the namespace of the
+                                                    // attribute NOT to test
                               nsIAtom* aAttribute, // attribute NOT to test
                               PRBool* const aDependence = nsnull) 
 
@@ -1322,9 +1324,9 @@ static PRBool SelectorMatches(RuleProcessorData &data,
       result = PR_TRUE;
       nsAttrSelector* attr = aSelector->mAttrList;
       do {
-        if (attr->mAttr == aAttribute) {
-          // XXX we should really have a namespace, not just an attr
-          // name, in HasAttributeDependentStyle!
+        if (attr->mAttr == aAttribute &&
+            (attr->mNameSpace == aNameSpaceID ||
+             attr->mNameSpace == kNameSpaceID_Unknown)) {
           result = PR_TRUE;
           if (aDependence)
             *aDependence = PR_TRUE;
@@ -1396,8 +1398,9 @@ static PRBool SelectorMatches(RuleProcessorData &data,
   if (result && IDList) {
     // test for ID match
     result = PR_FALSE;
-
-    if (aAttribute && aAttribute == data.mContent->GetIDAttributeName()) {
+    PRInt32 namespaceID;
+    if (aAttribute &&
+        data.mContent->IsPotentialIDAttributeName(namespaceID, aAttribute)) {
       result = PR_TRUE;
       if (aDependence)
         *aDependence = PR_TRUE;
@@ -1435,7 +1438,8 @@ static PRBool SelectorMatches(RuleProcessorData &data,
     
   if (result && aSelector->mClassList) {
     // test for class match
-    if (aAttribute && aAttribute == data.mContent->GetClassAttributeName()) {
+    if (aAttribute && aAttribute == data.mContent->GetClassAttributeName() &&
+        aNameSpaceID == kNameSpaceID_None) {
       result = PR_TRUE;
       if (aDependence)
         *aDependence = PR_TRUE;
@@ -1462,7 +1466,7 @@ static PRBool SelectorMatches(RuleProcessorData &data,
     for (nsCSSSelector *negation = aSelector->mNegations;
          result && negation; negation = negation->mNegations) {
       PRBool dependence = PR_FALSE;
-      result = !SelectorMatches(data, negation, aStateMask,
+      result = !SelectorMatches(data, negation, aStateMask, aNameSpaceID,
                                 aAttribute, &dependence);
       // If the selector does match due to the dependence on aStateMask
       // or aAttribute, then we want to keep result true so that the
@@ -1536,7 +1540,7 @@ static PRBool SelectorMatchesTree(RuleProcessorData& aPrevData,
     if (! data) {
       return PR_FALSE;
     }
-    if (SelectorMatches(*data, selector, 0, nsnull)) {
+    if (SelectorMatches(*data, selector, 0, kNameSpaceID_Unknown, nsnull)) {
       // to avoid greedy matching, we need to recur if this is a
       // descendant combinator and the next combinator is not
       if ((NS_IS_GREEDY_OPERATOR(selector->mOperator)) &&
@@ -1573,7 +1577,7 @@ static void ContentEnumFunc(nsICSSStyleRule* aRule, nsCSSSelector* aSelector,
 {
   ElementRuleProcessorData* data = (ElementRuleProcessorData*)aData;
 
-  if (SelectorMatches(*data, aSelector, 0, nsnull)) {
+  if (SelectorMatches(*data, aSelector, 0, kNameSpaceID_Unknown, nsnull)) {
     nsCSSSelector *next = aSelector->mNext;
     if (!next || SelectorMatchesTree(*data, next)) {
       // for performance, require that every implementation of
@@ -1626,7 +1630,7 @@ static void PseudoEnumFunc(nsICSSStyleRule* aRule, nsCSSSelector* aSelector,
       if (PRUnichar('+') == selector->mOperator) {
         return; // not valid here, can't match
       }
-      if (SelectorMatches(*data, selector, 0, nsnull)) {
+      if (SelectorMatches(*data, selector, 0, kNameSpaceID_Unknown, nsnull)) {
         selector = selector->mNext;
       }
       else {
@@ -1697,7 +1701,8 @@ PR_STATIC_CALLBACK(PRBool) StateEnumFunc(void* aSelector, void* aData)
   // bother calling SelectorMatches, since even if it returns false
   // enumData->change won't change.
   if ((possibleChange & ~(enumData->change)) &&
-      SelectorMatches(*data, selector, data->mStateMask, nsnull) &&
+      SelectorMatches(*data, selector, data->mStateMask, kNameSpaceID_Unknown,
+                      nsnull) &&
       SelectorMatchesTree(*data, selector->mNext)) {
     enumData->change = nsReStyleHint(enumData->change | possibleChange);
   }
@@ -1751,7 +1756,8 @@ PR_STATIC_CALLBACK(PRBool) AttributeEnumFunc(void* aSelector, void* aData)
   // bother calling SelectorMatches, since even if it returns false
   // enumData->change won't change.
   if ((possibleChange & ~(enumData->change)) &&
-      SelectorMatches(*data, selector, data->mStateMask, data->mAttribute) &&
+      SelectorMatches(*data, selector, data->mStateMask, data->mNameSpaceID,
+                      data->mAttribute) &&
       SelectorMatchesTree(*data, selector->mNext)) {
     enumData->change = nsReStyleHint(enumData->change | possibleChange);
   }
@@ -1772,6 +1778,7 @@ nsCSSRuleProcessor::HasAttributeDependentStyle(AttributeRuleProcessorData* aData
   // and :visited rules from prefs), rather than hacking AddRule below
   // to add |href| to the hash, we'll just handle it here.
   if (aData->mAttribute == nsGkAtoms::href &&
+      aData->mNameSpaceID == kNameSpaceID_None &&
       aData->mIsHTMLContent &&
       (aData->mContentTag == nsGkAtoms::a ||
        aData->mContentTag == nsGkAtoms::area ||
@@ -1789,11 +1796,13 @@ nsCSSRuleProcessor::HasAttributeDependentStyle(AttributeRuleProcessorData* aData
   // we have a hashtable with a per-attribute list.
 
   if (cascade) {
-    if (aData->mAttribute == aData->mContent->GetIDAttributeName()) {
+    if (aData->mContent->IsPotentialIDAttributeName(aData->mNameSpaceID,
+                                                    aData->mAttribute)) {
       cascade->mIDSelectors.EnumerateForwards(AttributeEnumFunc, &data);
     }
     
-    if (aData->mAttribute == aData->mContent->GetClassAttributeName()) {
+    if (aData->mNameSpaceID == kNameSpaceID_None &&
+        aData->mAttribute == aData->mContent->GetClassAttributeName()) {
       cascade->mClassSelectors.EnumerateForwards(AttributeEnumFunc, &data);
     }
 
diff --git a/layout/style/nsIStyleRuleProcessor.h b/layout/style/nsIStyleRuleProcessor.h
index e0224d6f40c..6569470f701 100644
--- a/layout/style/nsIStyleRuleProcessor.h
+++ b/layout/style/nsIStyleRuleProcessor.h
@@ -153,19 +153,24 @@ struct StateRuleProcessorData : public RuleProcessorData {
 struct AttributeRuleProcessorData : public RuleProcessorData {
   AttributeRuleProcessorData(nsPresContext* aPresContext,
                              nsIContent* aContent,
+                             PRInt32 aNameSpaceID,
                              nsIAtom* aAttribute,
                              PRInt32 aModType,
                              PRUint32 aStateMask)
     : RuleProcessorData(aPresContext, aContent, nsnull),
+      mNameSpaceID(aNameSpaceID),
       mAttribute(aAttribute),
       mModType(aModType),
       mStateMask(aStateMask)
   {
     NS_PRECONDITION(aContent, "null pointer");
   }
-  nsIAtom* mAttribute; // |HasAttributeDependentStyle| for which attribute?
-  PRInt32 mModType;    // The type of modification (see nsIDOMMutationEvent).
-  PRUint32 mStateMask; // The states that changed with the attr change.
+  // |HasAttributeDependentStyle| for which attribute?
+  PRInt32  mNameSpaceID;
+  nsIAtom* mAttribute;
+
+  PRInt32  mModType;     // The type of modification (see nsIDOMMutationEvent).
+  PRUint32 mStateMask;   // The states that changed with the attr change.
 };
 
 
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index 3c21988e503..35133d96c5b 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -959,10 +959,10 @@ nsStyleSet::HasStateDependentStyle(nsPresContext* aPresContext,
 
 struct AttributeData : public AttributeRuleProcessorData {
   AttributeData(nsPresContext* aPresContext,
-                nsIContent* aContent, nsIAtom* aAttribute, PRInt32 aModType,
-                PRUint32 aStateMask)
-    : AttributeRuleProcessorData(aPresContext, aContent, aAttribute, aModType,
-                                 aStateMask),
+                nsIContent* aContent, PRInt32 aNameSpaceID,
+                nsIAtom* aAttribute, PRInt32 aModType, PRUint32 aStateMask)
+    : AttributeRuleProcessorData(aPresContext, aContent, aNameSpaceID,
+                                 aAttribute, aModType, aStateMask),
       mHint(nsReStyleHint(0))
   {}
   nsReStyleHint   mHint;
@@ -982,6 +982,7 @@ SheetHasAttributeStyle(nsIStyleRuleProcessor* aProcessor, void *aData)
 nsReStyleHint
 nsStyleSet::HasAttributeDependentStyle(nsPresContext* aPresContext,
                                        nsIContent*    aContent,
+                                       PRInt32        aNameSpaceID,
                                        nsIAtom*       aAttribute,
                                        PRInt32        aModType,
                                        PRUint32       aStateMask)
@@ -996,8 +997,8 @@ nsStyleSet::HasAttributeDependentStyle(nsPresContext* aPresContext,
        mRuleProcessors[eDocSheet]          ||
        mRuleProcessors[eStyleAttrSheet]    ||
        mRuleProcessors[eOverrideSheet])) {
-    AttributeData data(aPresContext, aContent, aAttribute, aModType,
-                       aStateMask);
+    AttributeData data(aPresContext, aContent, aNameSpaceID, aAttribute,
+                       aModType, aStateMask);
     WalkRuleProcessors(SheetHasAttributeStyle, &data);
     result = data.mHint;
   }
diff --git a/layout/style/nsStyleSet.h b/layout/style/nsStyleSet.h
index 69bb6dc6af1..bbd8992fc72 100644
--- a/layout/style/nsStyleSet.h
+++ b/layout/style/nsStyleSet.h
@@ -139,6 +139,7 @@ class nsStyleSet
   // Test if style is dependent on the presence of an attribute.
   nsReStyleHint HasAttributeDependentStyle(nsPresContext* aPresContext,
                                            nsIContent*    aContent,
+                                           PRInt32        aNameSpaceID,
                                            nsIAtom*       aAttribute,
                                            PRInt32        aModType,
                                            PRUint32       aStateMask);
diff --git a/layout/style/test/Makefile.in b/layout/style/test/Makefile.in
index c9dc3ac1dbf..c7fada50039 100644
--- a/layout/style/test/Makefile.in
+++ b/layout/style/test/Makefile.in
@@ -68,6 +68,7 @@ css_properties.js: host_ListCSSProperties$(HOST_BIN_SUFFIX) css_properties_like_
 
 _TEST_FILES =	test_bug74880.html \
 		test_bug221428.html \
+		test_bug275196.xhtml \
 		test_bug302186.html \
 		test_bug319381.html \
 		test_bug357614.html \
diff --git a/layout/style/test/test_bug275196.xhtml b/layout/style/test/test_bug275196.xhtml
new file mode 100644
index 00000000000..747afa7692f
--- /dev/null
+++ b/layout/style/test/test_bug275196.xhtml
@@ -0,0 +1,149 @@
+<?xml version="1.0"?>
+<html xmlns="http://www.w3.org/1999/xhtml"
+      xmlns:foo="http://example.org/2005/02/13/#foo"
+      xml:id="start">
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=275196
+-->
+<head>
+  <title>Test for Bug 275196</title>
+  <script type="text/javascript" src="/MochiKit/packed.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    <style type="text/css">
+      :root {
+        background: red;
+      }
+
+      :root#foo {
+         background: rgb(0, 255, 0);
+      }
+
+      :root#bar {
+        background: rgb(0, 0, 255);
+      }
+
+      *[*|green] {
+        background: rgb(0, 255, 0);
+      }
+
+      #xhtml3, #foo2 {
+        background: rgb(0, 255, 0);
+      }
+    </style>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=275196">Mozilla Bug 275196</a>
+<p id="display"></p>
+<div id="content">
+  <div id="xhtml1" green="true">Element in XHTML namespace, attribute in null namespace</div>
+  <div id="xhtml2" foo:green="true">Element in XHTML namespace, attribute in foo namespace</div>
+  <foo:foo xml:id="foo1" foo:green="true">Element in foo namespace, attribute in foo namespace</foo:foo>
+  <div id="xhtml3">Element in XHTML namespace, id attribute</div>
+  <foo:foo xml:id="foo2">Element in foo namespace, xml:id attribute</foo:foo>
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+<![CDATA[
+
+/** Test for Bug 275196 **/
+
+// Test whether setting 'native' ID overrides xml:id
+function test_1() {
+  try {
+    document.getElementById('start').setAttribute('id', 'bar');
+  } catch (e) {
+    ok(false, "Couldn't find element 'start'");
+    test_2();
+    return;
+  }
+  ok(document.defaultView.getComputedStyle(document.documentElement, null).
+       getPropertyValue('background-color') == "rgb(0, 0, 255)",
+     "The background of the documentElement should be blue.");
+  test_2();
+}
+
+// Test if ID 'start' was removed from the document when the ID was set to 'bar'.
+function test_2() {
+  ok(document.getElementById('bar') != document.getElementById('start'),
+     "Element with ID 'bar' shouldn't be the same as 'start'");
+  test_3();
+}
+
+// Setting xml:id and removing 'native' ID
+function test_3() {
+  var b = null;
+  try {
+    b = document.getElementById('bar');
+    b.setAttributeNS("http://www.w3.org/XML/1998/namespace", "xml:id", "foo");
+    b.removeAttribute('id');
+  } catch (e) {
+    ok(false, e);
+    test_4();
+    return;
+  }
+  ok(document.defaultView.getComputedStyle(document.documentElement, null).
+       getPropertyValue('background-color') == "rgb(0, 255, 0)",
+     "The background of the documentElement should be green.");
+  test_4();
+}
+
+// Setting 'native' ID
+function test_4() {
+  try {
+    document.getElementById('foo').setAttribute('id', 'bar');
+  } catch (e) {
+    ok(false, e);
+    test_5();
+    return;
+  }
+  ok(document.defaultView.getComputedStyle(document.documentElement, null).
+       getPropertyValue('background-color') == "rgb(0, 0, 255)",
+     "The background of the documentElement should be blue.");
+  test_5();
+}
+
+function testElementBackground(elementId) {
+  var el = document.getElementById(elementId);
+  ok(document.defaultView.getComputedStyle(el, null).
+       getPropertyValue('background-color') == "rgb(0, 255, 0)",
+     "The background of the element should be green.");
+
+  el.removeAttribute("green");
+  el.removeAttributeNS("http://example.org/2005/02/13/#foo", "green");
+  ok(document.defaultView.getComputedStyle(el, null).
+       getPropertyValue('background-color') == "transparent",
+     "The element should have transparent background.");
+}
+
+// Test *[*|green] style rule.
+function test_5() {
+  testElementBackground("xhtml1");
+  testElementBackground("xhtml2");
+  testElementBackground("foo1");
+  test_6();
+}
+
+// Test #xhtml3, #foo2 style rule.
+function test_6() {
+  var el = document.getElementById("xhtml3");
+  ok(document.defaultView.getComputedStyle(el, null).
+       getPropertyValue('background-color') == "rgb(0, 255, 0)",
+     "The background of the element should be green.");
+
+  el = document.getElementById("foo2");
+  ok(document.defaultView.getComputedStyle(el, null).
+       getPropertyValue('background-color') == "rgb(0, 255, 0)",
+     "The background of the element should be green.");
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(test_1);
+
+]]>
+</script>
+</pre>
+</body>
+</html>
+