--- a/content/events/public/nsEventStates.h
+++ b/content/events/public/nsEventStates.h
@@ -254,15 +254,17 @@ private:
 // Handler for the content has crashed
 #define NS_EVENT_STATE_HANDLER_CRASHED NS_DEFINE_EVENT_STATE_MACRO(28)
 // Content has focus and should show a ring.
 #define NS_EVENT_STATE_FOCUSRING     NS_DEFINE_EVENT_STATE_MACRO(29)
 // Content shows its placeholder
 #define NS_EVENT_STATE_MOZ_PLACEHOLDER NS_DEFINE_EVENT_STATE_MACRO(30)
 // Content is a submit control and the form isn't valid.
 #define NS_EVENT_STATE_MOZ_SUBMITINVALID NS_DEFINE_EVENT_STATE_MACRO(31)
+// UI friendly version of :invalid pseudo-class.
+#define NS_EVENT_STATE_MOZ_UI_INVALID NS_DEFINE_EVENT_STATE_MACRO(32)
 
 /**
  * NOTE: do not go over 63 without updating nsEventStates::InternalType!
  */
 
 #endif // nsEventStates_h__
 

--- a/layout/style/nsCSSPseudoClassList.h
+++ b/layout/style/nsCSSPseudoClassList.h
@@ -177,13 +177,15 @@ CSS_STATE_PSEUDO_CLASS(defaultPseudo, ":
 CSS_STATE_PSEUDO_CLASS(mozReadOnly, ":-moz-read-only",
                        NS_EVENT_STATE_MOZ_READONLY)
 CSS_STATE_PSEUDO_CLASS(mozReadWrite, ":-moz-read-write",
                        NS_EVENT_STATE_MOZ_READWRITE)
 CSS_STATE_PSEUDO_CLASS(mozPlaceholder, ":-moz-placeholder",
                        NS_EVENT_STATE_MOZ_PLACEHOLDER)
 CSS_STATE_PSEUDO_CLASS(mozSubmitInvalid, ":-moz-submit-invalid",
                        NS_EVENT_STATE_MOZ_SUBMITINVALID)
+CSS_STATE_PSEUDO_CLASS(mozUIInvalid, ":-moz-ui-invalid",
+                       NS_EVENT_STATE_MOZ_UI_INVALID)
 
 #ifdef DEFINED_CSS_STATE_PSEUDO_CLASS
 #undef DEFINED_CSS_STATE_PSEUDO_CLASS
 #undef CSS_STATE_PSEUDO_CLASS
 #endif