diff --git a/mozilla/content/html/style/public/nsICSSStyleSheet.h b/mozilla/content/html/style/public/nsICSSStyleSheet.h
index 54291710ec0..a4f82f060bf 100644
--- a/mozilla/content/html/style/public/nsICSSStyleSheet.h
+++ b/mozilla/content/html/style/public/nsICSSStyleSheet.h
@@ -55,6 +55,8 @@ public:
 
   // get head of namespace chain for sheet
   NS_IMETHOD  GetNameSpace(nsINameSpace*& aNameSpace) const = 0;
+  // set default namespace for sheet (may be overridden by @namespace)
+  NS_IMETHOD  SetDefaultNameSpaceID(PRInt32 aDefaultNameSpaceID) = 0;
 
   NS_IMETHOD  Clone(nsICSSStyleSheet*& aClone) const = 0;
 
diff --git a/mozilla/layout/html/style/public/nsICSSStyleSheet.h b/mozilla/layout/html/style/public/nsICSSStyleSheet.h
index 54291710ec0..a4f82f060bf 100644
--- a/mozilla/layout/html/style/public/nsICSSStyleSheet.h
+++ b/mozilla/layout/html/style/public/nsICSSStyleSheet.h
@@ -55,6 +55,8 @@ public:
 
   // get head of namespace chain for sheet
   NS_IMETHOD  GetNameSpace(nsINameSpace*& aNameSpace) const = 0;
+  // set default namespace for sheet (may be overridden by @namespace)
+  NS_IMETHOD  SetDefaultNameSpaceID(PRInt32 aDefaultNameSpaceID) = 0;
 
   NS_IMETHOD  Clone(nsICSSStyleSheet*& aClone) const = 0;
 
diff --git a/mozilla/layout/style/nsICSSStyleSheet.h b/mozilla/layout/style/nsICSSStyleSheet.h
index 54291710ec0..a4f82f060bf 100644
--- a/mozilla/layout/style/nsICSSStyleSheet.h
+++ b/mozilla/layout/style/nsICSSStyleSheet.h
@@ -55,6 +55,8 @@ public:
 
   // get head of namespace chain for sheet
   NS_IMETHOD  GetNameSpace(nsINameSpace*& aNameSpace) const = 0;
+  // set default namespace for sheet (may be overridden by @namespace)
+  NS_IMETHOD  SetDefaultNameSpaceID(PRInt32 aDefaultNameSpaceID) = 0;
 
   NS_IMETHOD  Clone(nsICSSStyleSheet*& aClone) const = 0;