diff --git a/mozilla/string/obsolete/nsStr.cpp b/mozilla/string/obsolete/nsStr.cpp
index 087c73f389d..98d856c27ea 100644
--- a/mozilla/string/obsolete/nsStr.cpp
+++ b/mozilla/string/obsolete/nsStr.cpp
@@ -600,6 +600,7 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   mBuffer=aString;
   mCharSize=eOneByte;
   mStackBased=aStackBased;
+  mIsConst=PR_FALSE;
   mLength=mCapacity=0;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
@@ -609,11 +610,27 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   }
 }
 
+CBufDescriptor::CBufDescriptor(const char* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eOneByte;
+  mStackBased=aStackBased;
+  mIsConst=PR_TRUE;
+  mLength=mCapacity=0;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
+
+
 CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
   mBuffer=(char*)aString;
   mCharSize=eTwoByte;
   mStackBased=aStackBased;
   mLength=mCapacity=0;
+  mIsConst=PR_FALSE;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
     mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
@@ -622,5 +639,18 @@ CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aC
   }
 }
 
+CBufDescriptor::CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eTwoByte;
+  mStackBased=aStackBased;
+  mLength=mCapacity=0;
+  mIsConst=PR_TRUE;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/string/obsolete/nsStr.h b/mozilla/string/obsolete/nsStr.h
index daf814e797e..5f194705a99 100644
--- a/mozilla/string/obsolete/nsStr.h
+++ b/mozilla/string/obsolete/nsStr.h
@@ -183,15 +183,17 @@ class nsIMemoryAgent;
 
 class NS_COM CBufDescriptor {
 public:
-  CBufDescriptor(char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
-  CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(char* aString,           PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(PRUnichar* aString,      PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
 
   char*     mBuffer;
   eCharSize mCharSize;
   PRUint32  mCapacity;
   PRInt32   mLength;
   PRBool    mStackBased;
-
+  PRBool    mIsConst;
 };
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/string/obsolete/nsString.cpp b/mozilla/string/obsolete/nsString.cpp
index b3a868dcca8..1b9109be5d6 100644
--- a/mozilla/string/obsolete/nsString.cpp
+++ b/mozilla/string/obsolete/nsString.cpp
@@ -1753,7 +1753,8 @@ nsCAutoString::nsCAutoString(const CBufDescriptor& aBuffer) : nsCString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
 }
 
 /**
diff --git a/mozilla/string/obsolete/nsString2.cpp b/mozilla/string/obsolete/nsString2.cpp
index 58efcd34710..2049c9d1b17 100644
--- a/mozilla/string/obsolete/nsString2.cpp
+++ b/mozilla/string/obsolete/nsString2.cpp
@@ -109,6 +109,7 @@ nsString::nsString(const nsString& aString) :mAgent(aString.mAgent) {
  * @param   reference to a subsumeString
  */
 nsString::nsString(nsSubsumeStr& aSubsumeStr) :mAgent(0) {
+  nsStr::Initialize(*this,eTwoByte);
   Subsume(*this,aSubsumeStr);
 }
 
@@ -2149,7 +2150,8 @@ nsAutoString::nsAutoString(const CBufDescriptor& aBuffer) : nsString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this);
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this);
 }
 
 
diff --git a/mozilla/xpcom/ds/nsStr.cpp b/mozilla/xpcom/ds/nsStr.cpp
index 087c73f389d..98d856c27ea 100644
--- a/mozilla/xpcom/ds/nsStr.cpp
+++ b/mozilla/xpcom/ds/nsStr.cpp
@@ -600,6 +600,7 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   mBuffer=aString;
   mCharSize=eOneByte;
   mStackBased=aStackBased;
+  mIsConst=PR_FALSE;
   mLength=mCapacity=0;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
@@ -609,11 +610,27 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   }
 }
 
+CBufDescriptor::CBufDescriptor(const char* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eOneByte;
+  mStackBased=aStackBased;
+  mIsConst=PR_TRUE;
+  mLength=mCapacity=0;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
+
+
 CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
   mBuffer=(char*)aString;
   mCharSize=eTwoByte;
   mStackBased=aStackBased;
   mLength=mCapacity=0;
+  mIsConst=PR_FALSE;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
     mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
@@ -622,5 +639,18 @@ CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aC
   }
 }
 
+CBufDescriptor::CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eTwoByte;
+  mStackBased=aStackBased;
+  mLength=mCapacity=0;
+  mIsConst=PR_TRUE;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/xpcom/ds/nsStr.h b/mozilla/xpcom/ds/nsStr.h
index daf814e797e..5f194705a99 100644
--- a/mozilla/xpcom/ds/nsStr.h
+++ b/mozilla/xpcom/ds/nsStr.h
@@ -183,15 +183,17 @@ class nsIMemoryAgent;
 
 class NS_COM CBufDescriptor {
 public:
-  CBufDescriptor(char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
-  CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(char* aString,           PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(PRUnichar* aString,      PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
 
   char*     mBuffer;
   eCharSize mCharSize;
   PRUint32  mCapacity;
   PRInt32   mLength;
   PRBool    mStackBased;
-
+  PRBool    mIsConst;
 };
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/xpcom/ds/nsString.cpp b/mozilla/xpcom/ds/nsString.cpp
index b3a868dcca8..1b9109be5d6 100644
--- a/mozilla/xpcom/ds/nsString.cpp
+++ b/mozilla/xpcom/ds/nsString.cpp
@@ -1753,7 +1753,8 @@ nsCAutoString::nsCAutoString(const CBufDescriptor& aBuffer) : nsCString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
 }
 
 /**
diff --git a/mozilla/xpcom/ds/nsString2.cpp b/mozilla/xpcom/ds/nsString2.cpp
index 58efcd34710..2049c9d1b17 100644
--- a/mozilla/xpcom/ds/nsString2.cpp
+++ b/mozilla/xpcom/ds/nsString2.cpp
@@ -109,6 +109,7 @@ nsString::nsString(const nsString& aString) :mAgent(aString.mAgent) {
  * @param   reference to a subsumeString
  */
 nsString::nsString(nsSubsumeStr& aSubsumeStr) :mAgent(0) {
+  nsStr::Initialize(*this,eTwoByte);
   Subsume(*this,aSubsumeStr);
 }
 
@@ -2149,7 +2150,8 @@ nsAutoString::nsAutoString(const CBufDescriptor& aBuffer) : nsString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this);
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this);
 }
 
 
diff --git a/mozilla/xpcom/string/obsolete/nsStr.cpp b/mozilla/xpcom/string/obsolete/nsStr.cpp
index 087c73f389d..98d856c27ea 100644
--- a/mozilla/xpcom/string/obsolete/nsStr.cpp
+++ b/mozilla/xpcom/string/obsolete/nsStr.cpp
@@ -600,6 +600,7 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   mBuffer=aString;
   mCharSize=eOneByte;
   mStackBased=aStackBased;
+  mIsConst=PR_FALSE;
   mLength=mCapacity=0;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
@@ -609,11 +610,27 @@ CBufDescriptor::CBufDescriptor(char* aString,PRBool aStackBased,PRUint32 aCapaci
   }
 }
 
+CBufDescriptor::CBufDescriptor(const char* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eOneByte;
+  mStackBased=aStackBased;
+  mIsConst=PR_TRUE;
+  mLength=mCapacity=0;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
+
+
 CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
   mBuffer=(char*)aString;
   mCharSize=eTwoByte;
   mStackBased=aStackBased;
   mLength=mCapacity=0;
+  mIsConst=PR_FALSE;
   if(aString && aCapacity>1) {
     mCapacity=aCapacity-1;
     mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
@@ -622,5 +639,18 @@ CBufDescriptor::CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aC
   }
 }
 
+CBufDescriptor::CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength) { 
+  mBuffer=(char*)aString;
+  mCharSize=eTwoByte;
+  mStackBased=aStackBased;
+  mLength=mCapacity=0;
+  mIsConst=PR_TRUE;
+  if(aString && aCapacity>1) {
+    mCapacity=aCapacity-1;
+    mLength=(-1==aLength) ? nsCRT::strlen(aString) : aLength;
+    if(mLength>PRInt32(mCapacity))
+      mLength=mCapacity;
+  }
+}
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/xpcom/string/obsolete/nsStr.h b/mozilla/xpcom/string/obsolete/nsStr.h
index daf814e797e..5f194705a99 100644
--- a/mozilla/xpcom/string/obsolete/nsStr.h
+++ b/mozilla/xpcom/string/obsolete/nsStr.h
@@ -183,15 +183,17 @@ class nsIMemoryAgent;
 
 class NS_COM CBufDescriptor {
 public:
-  CBufDescriptor(char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
-  CBufDescriptor(PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(char* aString,           PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const char* aString,     PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(PRUnichar* aString,      PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
+  CBufDescriptor(const PRUnichar* aString,PRBool aStackBased,PRUint32 aCapacity,PRInt32 aLength=-1);
 
   char*     mBuffer;
   eCharSize mCharSize;
   PRUint32  mCapacity;
   PRInt32   mLength;
   PRBool    mStackBased;
-
+  PRBool    mIsConst;
 };
 
 //----------------------------------------------------------------------------------------
diff --git a/mozilla/xpcom/string/obsolete/nsString.cpp b/mozilla/xpcom/string/obsolete/nsString.cpp
index b3a868dcca8..1b9109be5d6 100644
--- a/mozilla/xpcom/string/obsolete/nsString.cpp
+++ b/mozilla/xpcom/string/obsolete/nsString.cpp
@@ -1753,7 +1753,8 @@ nsCAutoString::nsCAutoString(const CBufDescriptor& aBuffer) : nsCString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this); //this isn't really needed, but it guarantees that folks don't pass string constants.
 }
 
 /**
diff --git a/mozilla/xpcom/string/obsolete/nsString2.cpp b/mozilla/xpcom/string/obsolete/nsString2.cpp
index 58efcd34710..2049c9d1b17 100644
--- a/mozilla/xpcom/string/obsolete/nsString2.cpp
+++ b/mozilla/xpcom/string/obsolete/nsString2.cpp
@@ -109,6 +109,7 @@ nsString::nsString(const nsString& aString) :mAgent(aString.mAgent) {
  * @param   reference to a subsumeString
  */
 nsString::nsString(nsSubsumeStr& aSubsumeStr) :mAgent(0) {
+  nsStr::Initialize(*this,eTwoByte);
   Subsume(*this,aSubsumeStr);
 }
 
@@ -2149,7 +2150,8 @@ nsAutoString::nsAutoString(const CBufDescriptor& aBuffer) : nsString() {
   else {
     nsStr::Initialize(*this,aBuffer.mBuffer,aBuffer.mCapacity,aBuffer.mLength,aBuffer.mCharSize,!aBuffer.mStackBased);
   }
-  AddNullTerminator(*this);
+  if(!aBuffer.mIsConst)
+    AddNullTerminator(*this);
 }