diff --git a/content/events/public/nsIEventStateManager.h b/content/events/public/nsIEventStateManager.h
index 0c39c4ad2c6e..54e5fe7d71cb 100644
--- a/content/events/public/nsIEventStateManager.h
+++ b/content/events/public/nsIEventStateManager.h
@@ -139,12 +139,17 @@ public:
   NS_IMETHOD ShiftFocus(PRBool aDirection, nsIContent* aStart)=0;
 };
 
-#define NS_EVENT_STATE_ACTIVE       0x0001 // mouse is down on content
-#define NS_EVENT_STATE_FOCUS        0x0002 // content has focus
-#define NS_EVENT_STATE_HOVER        0x0004 // mouse is hovering over content
-#define NS_EVENT_STATE_DRAGOVER     0x0008 // drag  is hovering over content
-#define NS_EVENT_STATE_URLTARGET    0x0010 // content is URL's target (ref)
+#define NS_EVENT_STATE_ACTIVE       0x00000001 // mouse is down on content
+#define NS_EVENT_STATE_FOCUS        0x00000002 // content has focus
+#define NS_EVENT_STATE_HOVER        0x00000004 // mouse is hovering over content
+#define NS_EVENT_STATE_DRAGOVER     0x00000008 // drag  is hovering over content
+#define NS_EVENT_STATE_URLTARGET    0x00000010 // content is URL's target (ref)
+
 // The following states are used only for ContentStatesChanged
-#define NS_EVENT_STATE_CHECKED      0x0020
+// CSS 3 Selectors
+#define NS_EVENT_STATE_CHECKED      0x00000020
+// CSS 3 UI
+#define NS_EVENT_STATE_REQUIRED     0x00000040
+#define NS_EVENT_STATE_OPTIONAL     0x00000080
 
 #endif // nsIEventStateManager_h__
diff --git a/layout/style/nsCSSPseudoClassList.h b/layout/style/nsCSSPseudoClassList.h
index d914facc3fb8..158d7dcd1761 100644
--- a/layout/style/nsCSSPseudoClassList.h
+++ b/layout/style/nsCSSPseudoClassList.h
@@ -76,3 +76,7 @@ CSS_PSEUDO_CLASS(lastChild, ":last-child")
 CSS_PSEUDO_CLASS(lastNode, ":-moz-last-node")
 CSS_PSEUDO_CLASS(onlyChild, ":only-child")
 
+// CSS 3 UI
+// http://www.w3.org/TR/2004/CR-css3-ui-20040511/#pseudo-classes
+CSS_PSEUDO_CLASS(required, ":required")
+CSS_PSEUDO_CLASS(optional, ":optional")
diff --git a/layout/style/nsCSSStyleSheet.cpp b/layout/style/nsCSSStyleSheet.cpp
index 93c7b307d922..1ca46ac4bd63 100644
--- a/layout/style/nsCSSStyleSheet.cpp
+++ b/layout/style/nsCSSStyleSheet.cpp
@@ -3125,6 +3125,12 @@ static PRBool SelectorMatches(RuleProcessorData &data,
       //  <input type=radio>
       result = STATE_CHECK(NS_EVENT_STATE_CHECKED);
     }
+    else if (nsCSSPseudoClasses::required == pseudoClass->mAtom) {
+      result = STATE_CHECK(NS_EVENT_STATE_REQUIRED);
+    }
+    else if (nsCSSPseudoClasses::optional == pseudoClass->mAtom) {
+      result = STATE_CHECK(NS_EVENT_STATE_OPTIONAL);
+    }
     else {
       NS_ERROR("CSS parser parsed a pseudo-class that we do not handle");
       result = PR_FALSE;  // unknown pseudo class
@@ -3637,7 +3643,9 @@ PRBool IsStateSelector(nsCSSSelector& aSelector)
         (pseudoClass->mAtom == nsCSSPseudoClasses::mozDragOver) || 
         (pseudoClass->mAtom == nsCSSPseudoClasses::focus) || 
         (pseudoClass->mAtom == nsCSSPseudoClasses::hover) ||
-        (pseudoClass->mAtom == nsCSSPseudoClasses::target)) {
+        (pseudoClass->mAtom == nsCSSPseudoClasses::target) ||
+        (pseudoClass->mAtom == nsCSSPseudoClasses::required) ||
+        (pseudoClass->mAtom == nsCSSPseudoClasses::optional)) {
       return PR_TRUE;
     }
   }