diff --git a/mozilla/xpcom/string/public/nsAString.h b/mozilla/xpcom/string/public/nsAString.h
index 4ad7eac140b..ccfb342477c 100644
--- a/mozilla/xpcom/string/public/nsAString.h
+++ b/mozilla/xpcom/string/public/nsAString.h
@@ -51,6 +51,11 @@
 #include "nsObsoleteAString.h"
 #endif
 
+// If some platform(s) can't handle our template that matches literal strings,
+// then we'll disable it on those platforms.
+// #define NS_DISABLE_LITERAL_TEMPLATE
+
+#include <string.h>
 
   // declare nsAString
 #include "string-template-def-unichar.h"
diff --git a/mozilla/xpcom/string/public/nsCharTraits.h b/mozilla/xpcom/string/public/nsCharTraits.h
index 872d38a67d2..00f05d19df8 100644
--- a/mozilla/xpcom/string/public/nsCharTraits.h
+++ b/mozilla/xpcom/string/public/nsCharTraits.h
@@ -62,6 +62,11 @@
   // for |PRUnichar|
 #endif
 
+#ifndef nsDebug_h__
+#include "nsDebug.h"
+  // for NS_ASSERTION
+#endif
+
 #ifdef HAVE_CPP_BOOL
   typedef bool nsCharTraits_bool;
 #else
@@ -181,6 +186,20 @@ struct nsCharTraits<PRUnichar>
 #endif
       }
 
+    static
+    int
+    compareASCII( const char_type* s1, const char* s2, size_t n )
+      {
+        for ( ; n--; ++s1, ++s2 )
+          {
+            NS_ASSERTION(!(*s2 & ~0x7F), "Unexpected non-ASCII character");
+            if ( !eq_int_type(to_int_type(*s1), to_int_type(*s2)) )
+              return to_int_type(*s1) - to_int_type(*s2);
+          }
+
+        return 0;
+      }
+
     static
     size_t
     length( const char_type* s )
@@ -332,6 +351,19 @@ struct nsCharTraits<char>
         return memcmp(s1, s2, n);
       }
 
+    static
+    int
+    compareASCII( const char_type* s1, const char* s2, size_t n )
+      {
+#ifdef DEBUG
+        for (size_t i = 0; i < n; ++i)
+          {
+            NS_ASSERTION(!(s2[i] & ~0x7F), "Unexpected non-ASCII character");
+          }
+#endif
+        return compare(s1, s2, n);
+      }
+
     static
     size_t
     length( const char_type* s )
diff --git a/mozilla/xpcom/string/public/nsSubstring.h b/mozilla/xpcom/string/public/nsSubstring.h
index fbb761569a7..0802f77aef5 100644
--- a/mozilla/xpcom/string/public/nsSubstring.h
+++ b/mozilla/xpcom/string/public/nsSubstring.h
@@ -45,6 +45,11 @@
 
 #define kNotFound -1
 
+// If some platform(s) can't handle our template that matches literal strings,
+// then we'll disable it on those platforms.
+// #define NS_DISABLE_LITERAL_TEMPLATE
+
+#include <string.h>
 
   // declare nsSubstring
 #include "string-template-def-unichar.h"
diff --git a/mozilla/xpcom/string/public/nsTAString.h b/mozilla/xpcom/string/public/nsTAString.h
index be565f183dc..53bc374cb15 100644
--- a/mozilla/xpcom/string/public/nsTAString.h
+++ b/mozilla/xpcom/string/public/nsTAString.h
@@ -197,6 +197,23 @@ class nsTAString_CharT
       NS_COM PRBool Equals( const char_type* ) const;
       NS_COM PRBool Equals( const char_type*, const comparator_type& ) const;
 
+        /**
+         * An efficient comparison with ASCII that can be used even for
+         * wide strings.
+         */
+      NS_COM PRBool EqualsASCII( const char* data, size_type len ) const;
+#ifdef NS_DISABLE_LITERAL_TEMPLATE
+      inline PRBool EqualsLiteral( const char* str ) const
+        {
+          return EqualsASCII(str, strlen(str));
+        }
+#else
+      template<int N>
+      inline PRBool EqualsLiteral( const char (&str)[N] ) const
+        {
+          return EqualsASCII(str, N-1);
+        }
+#endif
 
         /**
          * A string always references a non-null data pointer.  In some
diff --git a/mozilla/xpcom/string/public/nsTSubstring.h b/mozilla/xpcom/string/public/nsTSubstring.h
index 218d69f6276..7aca6c6a4ea 100644
--- a/mozilla/xpcom/string/public/nsTSubstring.h
+++ b/mozilla/xpcom/string/public/nsTSubstring.h
@@ -215,6 +215,19 @@ class nsTSubstring_CharT : public nsTAString_CharT
       NS_COM PRBool Equals( const char_type* data ) const;
       NS_COM PRBool Equals( const char_type* data, const comparator_type& comp ) const;
 
+      NS_COM PRBool EqualsASCII( const char* data, size_type len ) const;
+#ifdef NS_DISABLE_LITERAL_TEMPLATE
+      inline PRBool EqualsLiteral( const char* str ) const
+        {
+          return EqualsASCII(str, strlen(str));
+        }
+#else
+      template<int N>
+      inline PRBool EqualsLiteral( const char (&str)[N] ) const
+        {
+          return EqualsASCII(str, N-1);
+        }
+#endif
 
         /**
          * assignment
diff --git a/mozilla/xpcom/string/src/nsTAString.cpp b/mozilla/xpcom/string/src/nsTAString.cpp
index b01a0666d98..bd0aa3c0bf4 100644
--- a/mozilla/xpcom/string/src/nsTAString.cpp
+++ b/mozilla/xpcom/string/src/nsTAString.cpp
@@ -105,6 +105,15 @@ nsTAString_CharT::Equals( const char_type* data, const comparator_type& comparat
     return ToSubstring().Equals(data, comparator);
   }
 
+PRBool
+nsTAString_CharT::EqualsASCII( const char* data, size_type len ) const
+  {
+    if (mVTable == obsolete_string_type::sCanonicalVTable)
+      return AsSubstring()->EqualsASCII(data, len);
+
+    return ToSubstring().EqualsASCII(data, len);
+  }
+
 PRBool
 nsTAString_CharT::IsVoid() const
   {
diff --git a/mozilla/xpcom/string/src/nsTSubstring.cpp b/mozilla/xpcom/string/src/nsTSubstring.cpp
index be331f2e835..d457959290f 100644
--- a/mozilla/xpcom/string/src/nsTSubstring.cpp
+++ b/mozilla/xpcom/string/src/nsTSubstring.cpp
@@ -555,6 +555,12 @@ nsTSubstring_CharT::Equals( const char_type* data, const comparator_type& comp )
     return mLength == length && comp(mData, data, mLength) == 0;
   }
 
+PRBool
+nsTSubstring_CharT::EqualsASCII( const char* data, size_type len ) const
+  {
+    return mLength == len && char_traits::compareASCII(mData, data, len) == 0;
+  }
+
 nsTSubstring_CharT::size_type
 nsTSubstring_CharT::CountChar( char_type c ) const
   {