diff --git a/htmlparser/src/nsIParser.h b/htmlparser/src/nsIParser.h
index 08f99b4d5f35..13af74172485 100644
--- a/htmlparser/src/nsIParser.h
+++ b/htmlparser/src/nsIParser.h
@@ -167,7 +167,7 @@ class nsIParser : public nsISupports {
     virtual nsresult	Parse(nsIInputStream& aStream, PRBool aEnableVerify=PR_FALSE, void* aKey=0) = 0;
     virtual nsresult  Parse(nsString& aSourceBuffer,void* aKey,const nsString& aContentType,PRBool aEnableVerify,PRBool aLastCall) = 0;
 
-    virtual PRBool    IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
+    virtual PRBool    IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
     virtual nsresult  ParseFragment(nsString& aSourceBuffer,void* aKey,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
 
     /**
diff --git a/htmlparser/src/nsParser.cpp b/htmlparser/src/nsParser.cpp
index bff09a56642c..cad0057fbcd9 100644
--- a/htmlparser/src/nsParser.cpp
+++ b/htmlparser/src/nsParser.cpp
@@ -794,7 +794,7 @@ nsresult nsParser::Parse(nsString& aSourceBuffer,void* aKey,const nsString& aCon
  *  @param   
  *  @return  
  */
-PRBool nsParser::IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType){
+PRBool nsParser::IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType){
   PRBool result=PR_FALSE;
   return result;
 }
diff --git a/htmlparser/src/nsParser.h b/htmlparser/src/nsParser.h
index 5f0872e04891..78a4da0e0a39 100644
--- a/htmlparser/src/nsParser.h
+++ b/htmlparser/src/nsParser.h
@@ -184,7 +184,7 @@ friend class CTokenHandler;
     virtual nsresult Parse(nsString& aSourceBuffer,void* aKey,const nsString& aContentType,PRBool aEnableVerify=PR_FALSE,PRBool aLastCall=PR_FALSE);
 
 
-    virtual PRBool    IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);
+    virtual PRBool    IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);
     virtual nsresult  ParseFragment(nsString& aSourceBuffer,void* aKey,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);
 
 
diff --git a/parser/htmlparser/src/nsIParser.h b/parser/htmlparser/src/nsIParser.h
index 08f99b4d5f35..13af74172485 100644
--- a/parser/htmlparser/src/nsIParser.h
+++ b/parser/htmlparser/src/nsIParser.h
@@ -167,7 +167,7 @@ class nsIParser : public nsISupports {
     virtual nsresult	Parse(nsIInputStream& aStream, PRBool aEnableVerify=PR_FALSE, void* aKey=0) = 0;
     virtual nsresult  Parse(nsString& aSourceBuffer,void* aKey,const nsString& aContentType,PRBool aEnableVerify,PRBool aLastCall) = 0;
 
-    virtual PRBool    IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
+    virtual PRBool    IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
     virtual nsresult  ParseFragment(nsString& aSourceBuffer,void* aKey,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType)=0;
 
     /**
diff --git a/parser/htmlparser/src/nsParser.cpp b/parser/htmlparser/src/nsParser.cpp
index bff09a56642c..cad0057fbcd9 100644
--- a/parser/htmlparser/src/nsParser.cpp
+++ b/parser/htmlparser/src/nsParser.cpp
@@ -794,7 +794,7 @@ nsresult nsParser::Parse(nsString& aSourceBuffer,void* aKey,const nsString& aCon
  *  @param   
  *  @return  
  */
-PRBool nsParser::IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType){
+PRBool nsParser::IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType){
   PRBool result=PR_FALSE;
   return result;
 }
diff --git a/parser/htmlparser/src/nsParser.h b/parser/htmlparser/src/nsParser.h
index 5f0872e04891..78a4da0e0a39 100644
--- a/parser/htmlparser/src/nsParser.h
+++ b/parser/htmlparser/src/nsParser.h
@@ -184,7 +184,7 @@ friend class CTokenHandler;
     virtual nsresult Parse(nsString& aSourceBuffer,void* aKey,const nsString& aContentType,PRBool aEnableVerify=PR_FALSE,PRBool aLastCall=PR_FALSE);
 
 
-    virtual PRBool    IsValidFragment(nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);
+    virtual PRBool    IsValidFragment(const nsString& aSourceBuffer,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);
     virtual nsresult  ParseFragment(nsString& aSourceBuffer,void* aKey,nsITagStack& aStack,PRUint32 anInsertPos,const nsString& aContentType);