diff --git a/mozilla/string/public/nsAReadableString.h b/mozilla/string/public/nsAReadableString.h
index 23223135ab6..e2dbad1e89c 100644
--- a/mozilla/string/public/nsAReadableString.h
+++ b/mozilla/string/public/nsAReadableString.h
@@ -1184,6 +1184,15 @@ class nsPromiseSubstring
           // nothing else to do here
         }
 
+      nsPromiseSubstring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+          : mString(*aStart.mOwningString)
+        {
+          nsReadingIterator<CharT> zeroPoint;
+          mOwningString.BeginReading(zeroPoint);
+          mStartPos = Distance(zeroPoint, aStart);
+          mLength = Distance(aStart, aEnd);
+        }
+
       // nsPromiseSubstring( const nsPromiseSubstring<CharT>& ); // auto-generated copy-constructor should be OK
       // ~nsPromiseSubstring();                                  // auto-generated destructor OK
 
@@ -1278,6 +1287,13 @@ Substring( const basic_nsAReadableString<CharT>& aString, PRUint32 aStartPos, PR
     return nsPromiseSubstring<CharT>(aString, aStartPos, aSubstringLength);
   }
 
+template <class CharT>
+nsPromiseSubstring<CharT>
+Substring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+  {
+    return nsPromiseSubstring<Chart>(aStart, aEnd);
+  }
+
 template <class CharT>
 int
 Compare( const basic_nsAReadableString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
diff --git a/mozilla/string/public/nsReadableUtils.h b/mozilla/string/public/nsReadableUtils.h
index a9f39d0b0e9..7b82e3fa4eb 100755
--- a/mozilla/string/public/nsReadableUtils.h
+++ b/mozilla/string/public/nsReadableUtils.h
@@ -35,6 +35,11 @@
 #include "nsAWritableString.h"
 #endif
 
+NS_COM size_t Distance( const nsReadingIterator<PRUnichar>&, const nsReadingIterator<PRUnichar>& );
+NS_COM size_t Distance( const nsReadingIterator<char>&, const nsReadingIterator<char>& );
+
+
+
 NS_COM void CopyUCS2toASCII( const nsAReadableString& aSource, nsAWritableCString& aDest );
 NS_COM void CopyASCIItoUCS2( const nsAReadableCString& aSource, nsAWritableString& aDest );
 
diff --git a/mozilla/string/src/nsReadableUtils.cpp b/mozilla/string/src/nsReadableUtils.cpp
index 5527e1e48c8..c67b2858b24 100755
--- a/mozilla/string/src/nsReadableUtils.cpp
+++ b/mozilla/string/src/nsReadableUtils.cpp
@@ -27,6 +27,45 @@
 #include "nsCRT.h"
 
 
+template <class CharT> class CalculateLength
+  {
+    public:
+      typedef CharT value_type;
+
+      CalculateLength() : mDistance(0) { }
+      size_t GetDistance() const       { return mDistance; }
+
+      PRUint32 write( const CharT*, PRUint32 N )
+                                       { mDistance += N; return N; }
+    private:
+      size_t mDistance;
+  };
+
+template <class CharT>
+inline
+size_t
+Distance_Impl( const nsReadingIterator<CharT>& aStart,
+          const nsReadingIterator<CharT>& aEnd )
+  {
+    CalculateLength<CharT> sink;
+    nsReadingIterator<CharT> fromBegin(aStart);
+    copy_string(fromBegin, aEnd, sink);
+    return sink.GetDistance();
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<PRUnichar>& aStart, const nsReadingIterator<PRUnichar>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<char>& aStart, const nsReadingIterator<char>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
 
 
 
diff --git a/mozilla/xpcom/ds/nsAReadableString.h b/mozilla/xpcom/ds/nsAReadableString.h
index 23223135ab6..e2dbad1e89c 100644
--- a/mozilla/xpcom/ds/nsAReadableString.h
+++ b/mozilla/xpcom/ds/nsAReadableString.h
@@ -1184,6 +1184,15 @@ class nsPromiseSubstring
           // nothing else to do here
         }
 
+      nsPromiseSubstring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+          : mString(*aStart.mOwningString)
+        {
+          nsReadingIterator<CharT> zeroPoint;
+          mOwningString.BeginReading(zeroPoint);
+          mStartPos = Distance(zeroPoint, aStart);
+          mLength = Distance(aStart, aEnd);
+        }
+
       // nsPromiseSubstring( const nsPromiseSubstring<CharT>& ); // auto-generated copy-constructor should be OK
       // ~nsPromiseSubstring();                                  // auto-generated destructor OK
 
@@ -1278,6 +1287,13 @@ Substring( const basic_nsAReadableString<CharT>& aString, PRUint32 aStartPos, PR
     return nsPromiseSubstring<CharT>(aString, aStartPos, aSubstringLength);
   }
 
+template <class CharT>
+nsPromiseSubstring<CharT>
+Substring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+  {
+    return nsPromiseSubstring<Chart>(aStart, aEnd);
+  }
+
 template <class CharT>
 int
 Compare( const basic_nsAReadableString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
diff --git a/mozilla/xpcom/ds/nsReadableUtils.cpp b/mozilla/xpcom/ds/nsReadableUtils.cpp
index 5527e1e48c8..c67b2858b24 100755
--- a/mozilla/xpcom/ds/nsReadableUtils.cpp
+++ b/mozilla/xpcom/ds/nsReadableUtils.cpp
@@ -27,6 +27,45 @@
 #include "nsCRT.h"
 
 
+template <class CharT> class CalculateLength
+  {
+    public:
+      typedef CharT value_type;
+
+      CalculateLength() : mDistance(0) { }
+      size_t GetDistance() const       { return mDistance; }
+
+      PRUint32 write( const CharT*, PRUint32 N )
+                                       { mDistance += N; return N; }
+    private:
+      size_t mDistance;
+  };
+
+template <class CharT>
+inline
+size_t
+Distance_Impl( const nsReadingIterator<CharT>& aStart,
+          const nsReadingIterator<CharT>& aEnd )
+  {
+    CalculateLength<CharT> sink;
+    nsReadingIterator<CharT> fromBegin(aStart);
+    copy_string(fromBegin, aEnd, sink);
+    return sink.GetDistance();
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<PRUnichar>& aStart, const nsReadingIterator<PRUnichar>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<char>& aStart, const nsReadingIterator<char>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
 
 
 
diff --git a/mozilla/xpcom/ds/nsReadableUtils.h b/mozilla/xpcom/ds/nsReadableUtils.h
index a9f39d0b0e9..7b82e3fa4eb 100755
--- a/mozilla/xpcom/ds/nsReadableUtils.h
+++ b/mozilla/xpcom/ds/nsReadableUtils.h
@@ -35,6 +35,11 @@
 #include "nsAWritableString.h"
 #endif
 
+NS_COM size_t Distance( const nsReadingIterator<PRUnichar>&, const nsReadingIterator<PRUnichar>& );
+NS_COM size_t Distance( const nsReadingIterator<char>&, const nsReadingIterator<char>& );
+
+
+
 NS_COM void CopyUCS2toASCII( const nsAReadableString& aSource, nsAWritableCString& aDest );
 NS_COM void CopyASCIItoUCS2( const nsAReadableCString& aSource, nsAWritableString& aDest );
 
diff --git a/mozilla/xpcom/string/public/nsAReadableString.h b/mozilla/xpcom/string/public/nsAReadableString.h
index 23223135ab6..e2dbad1e89c 100644
--- a/mozilla/xpcom/string/public/nsAReadableString.h
+++ b/mozilla/xpcom/string/public/nsAReadableString.h
@@ -1184,6 +1184,15 @@ class nsPromiseSubstring
           // nothing else to do here
         }
 
+      nsPromiseSubstring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+          : mString(*aStart.mOwningString)
+        {
+          nsReadingIterator<CharT> zeroPoint;
+          mOwningString.BeginReading(zeroPoint);
+          mStartPos = Distance(zeroPoint, aStart);
+          mLength = Distance(aStart, aEnd);
+        }
+
       // nsPromiseSubstring( const nsPromiseSubstring<CharT>& ); // auto-generated copy-constructor should be OK
       // ~nsPromiseSubstring();                                  // auto-generated destructor OK
 
@@ -1278,6 +1287,13 @@ Substring( const basic_nsAReadableString<CharT>& aString, PRUint32 aStartPos, PR
     return nsPromiseSubstring<CharT>(aString, aStartPos, aSubstringLength);
   }
 
+template <class CharT>
+nsPromiseSubstring<CharT>
+Substring( const nsReadingIterator<CharT>& aStart, const nsReadingIterator<CharT>& aEnd )
+  {
+    return nsPromiseSubstring<Chart>(aStart, aEnd);
+  }
+
 template <class CharT>
 int
 Compare( const basic_nsAReadableString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
diff --git a/mozilla/xpcom/string/public/nsReadableUtils.h b/mozilla/xpcom/string/public/nsReadableUtils.h
index a9f39d0b0e9..7b82e3fa4eb 100755
--- a/mozilla/xpcom/string/public/nsReadableUtils.h
+++ b/mozilla/xpcom/string/public/nsReadableUtils.h
@@ -35,6 +35,11 @@
 #include "nsAWritableString.h"
 #endif
 
+NS_COM size_t Distance( const nsReadingIterator<PRUnichar>&, const nsReadingIterator<PRUnichar>& );
+NS_COM size_t Distance( const nsReadingIterator<char>&, const nsReadingIterator<char>& );
+
+
+
 NS_COM void CopyUCS2toASCII( const nsAReadableString& aSource, nsAWritableCString& aDest );
 NS_COM void CopyASCIItoUCS2( const nsAReadableCString& aSource, nsAWritableString& aDest );
 
diff --git a/mozilla/xpcom/string/src/nsReadableUtils.cpp b/mozilla/xpcom/string/src/nsReadableUtils.cpp
index 5527e1e48c8..c67b2858b24 100755
--- a/mozilla/xpcom/string/src/nsReadableUtils.cpp
+++ b/mozilla/xpcom/string/src/nsReadableUtils.cpp
@@ -27,6 +27,45 @@
 #include "nsCRT.h"
 
 
+template <class CharT> class CalculateLength
+  {
+    public:
+      typedef CharT value_type;
+
+      CalculateLength() : mDistance(0) { }
+      size_t GetDistance() const       { return mDistance; }
+
+      PRUint32 write( const CharT*, PRUint32 N )
+                                       { mDistance += N; return N; }
+    private:
+      size_t mDistance;
+  };
+
+template <class CharT>
+inline
+size_t
+Distance_Impl( const nsReadingIterator<CharT>& aStart,
+          const nsReadingIterator<CharT>& aEnd )
+  {
+    CalculateLength<CharT> sink;
+    nsReadingIterator<CharT> fromBegin(aStart);
+    copy_string(fromBegin, aEnd, sink);
+    return sink.GetDistance();
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<PRUnichar>& aStart, const nsReadingIterator<PRUnichar>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<char>& aStart, const nsReadingIterator<char>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }