diff --git a/content/xslt/src/base/txURIUtils.cpp b/content/xslt/src/base/txURIUtils.cpp
index afd84a9ff280..4c205af627a6 100644
--- a/content/xslt/src/base/txURIUtils.cpp
+++ b/content/xslt/src/base/txURIUtils.cpp
@@ -154,7 +154,7 @@ void URIUtils::getDocumentBase(const nsAFlatString& href, nsAString& dest)
     PRUint32 iter = href.Length();
     while (iter > 0) {
         if (temp[--iter] == HREF_PATH_SEP) {
-            dest.Append(Substring(href, 0, iter));
+            dest.Append(StringHead(href, iter));
             break;
         }
     }
diff --git a/content/xslt/src/xpath/nsXPath1Scheme.cpp b/content/xslt/src/xpath/nsXPath1Scheme.cpp
index aa7bfd6e9c12..d75142a7dd83 100755
--- a/content/xslt/src/xpath/nsXPath1Scheme.cpp
+++ b/content/xslt/src/xpath/nsXPath1Scheme.cpp
@@ -116,7 +116,7 @@ nsXPath1SchemeNSResolver::LookupNamespaceURI(const nsAString &aPrefix,
     mContext->GetSchemeData(i, scheme, data);
     if (scheme.Equals(xmlns)) {
       PRInt32 sep = data.FindChar('=');
-      if (sep > 0 && aPrefix.Equals(Substring(data, 0, sep))) {
+      if (sep > 0 && aPrefix.Equals(StringHead(data, sep))) {
         aURI.Assign(Substring(data, sep + 1, data.Length() - sep - 1));
         return NS_OK;
       }
diff --git a/content/xslt/src/xpath/txCoreFunctionCall.cpp b/content/xslt/src/xpath/txCoreFunctionCall.cpp
index 221d8a34abec..509ee4adb4ce 100755
--- a/content/xslt/src/xpath/txCoreFunctionCall.cpp
+++ b/content/xslt/src/xpath/txCoreFunctionCall.cpp
@@ -662,10 +662,11 @@ txCoreFunctionCall::evaluate(txIEvalContext* aContext, txAExprResult** aResult)
             nsresult rv = param->evaluateToString(aContext, arg);
             NS_ENSURE_SUCCESS(rv, rv);
 
-            PRBool result = arg.Equals(Substring(lang, 0, arg.Length()),
-                                       txCaseInsensitiveStringComparator()) &&
-                            (lang.Length() == arg.Length() ||
-                             lang.CharAt(arg.Length()) == '-');
+            PRBool result =
+                StringBeginsWith(lang, arg,
+                                 txCaseInsensitiveStringComparator()) &&
+                (lang.Length() == arg.Length() ||
+                 lang.CharAt(arg.Length()) == '-');
 
             aContext->recycler()->getBoolResult(result, aResult);
 
diff --git a/content/xslt/src/xpath/txExprParser.cpp b/content/xslt/src/xpath/txExprParser.cpp
index 72306191b6be..1bfb3e21ddf5 100644
--- a/content/xslt/src/xpath/txExprParser.cpp
+++ b/content/xslt/src/xpath/txExprParser.cpp
@@ -916,7 +916,7 @@ txExprParser::resolveQName(const nsAString& aQName,
     aNamespace = kNameSpaceID_None;
     PRInt32 idx = aQName.FindChar(':');
     if (idx > 0) {
-        *aPrefix = NS_NewAtom(Substring(aQName, 0, (PRUint32)idx));
+        *aPrefix = NS_NewAtom(StringHead(aQName, (PRUint32)idx));
         if (!*aPrefix) {
             return NS_ERROR_OUT_OF_MEMORY;
         }
diff --git a/content/xslt/src/xslt/txStylesheetCompileHandlers.cpp b/content/xslt/src/xslt/txStylesheetCompileHandlers.cpp
index 0df6490ef225..2eba6354d507 100644
--- a/content/xslt/src/xslt/txStylesheetCompileHandlers.cpp
+++ b/content/xslt/src/xslt/txStylesheetCompileHandlers.cpp
@@ -1079,7 +1079,7 @@ txFnStartStripSpace(PRInt32 aNamespaceID,
                 if (c[length-2] != ':') {
                     return NS_ERROR_XSLT_PARSE_FAILURE;
                 }
-                rv = XMLUtils::splitQName(Substring(name, 0, length-2), 
+                rv = XMLUtils::splitQName(StringHead(name, length - 2), 
                                           getter_AddRefs(prefix),
                                           getter_AddRefs(localName));
                 if (NS_FAILED(rv) || prefix) {