--- a/startupcache/nsIStartupCache.idl
+++ b/startupcache/nsIStartupCache.idl
@@ -4,26 +4,42 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsIInputStream.idl"
 #include "nsISupports.idl"
 #include "nsIObserver.idl"
 #include "nsIObjectOutputStream.idl"
 
+%{C++
+#include "mozilla/UniquePtr.h"
+%}
+
 [uuid(25957820-90a1-428c-8739-b0845d3cc534)]
 interface nsIStartupCache : nsISupports
 {
 
   /** This interface is provided for testing purposes only, basically
    *  just to solve link vagaries. See docs in StartupCache.h
    *  GetBuffer, PutBuffer, and InvalidateCache act as described 
    *  in that file. */
 
   uint32_t getBuffer(in string aID, out charPtr aBuffer);
+%{C++
+  /* A more convenient interface for using from C++.  */
+  nsresult GetBuffer(const char* id, mozilla::UniquePtr<char[]>* outbuf, uint32_t* length)
+  {
+    char* buf;
+    nsresult rv = GetBuffer(id, &buf, length);
+    NS_ENSURE_SUCCESS(rv, rv);
+    outbuf->reset(buf);
+    return rv;
+  }
+%}
+
   void putBuffer(in string aID, in string aBuffer, 
                             in uint32_t aLength);
  
   void invalidateCache();
   
   void ignoreDiskCache();
 
   /** In debug builds, wraps this object output stream with a stream that will 

--- a/startupcache/test/TestStartupCache.cpp
+++ b/startupcache/test/TestStartupCache.cpp
@@ -87,36 +87,33 @@ TestStartupWriteRead() {
     return NS_ERROR_FAILURE;
   } else {
     passed("got a pointer?");
   }
   sc->InvalidateCache();
   
   const char* buf = "Market opportunities for BeardBook";
   const char* id = "id";
-  char* outbufPtr = nullptr;
-  nsAutoArrayPtr<char> outbuf;  
+  UniquePtr<char[]> outbuf;  
   uint32_t len;
   
   rv = sc->PutBuffer(id, buf, strlen(buf) + 1);
   NS_ENSURE_SUCCESS(rv, rv);
   
-  rv = sc->GetBuffer(id, &outbufPtr, &len);
+  rv = sc->GetBuffer(id, &outbuf, &len);
   NS_ENSURE_SUCCESS(rv, rv);
-  outbuf = outbufPtr;
-  NS_ENSURE_STR_MATCH(buf, outbuf, "pre-write read");
+  NS_ENSURE_STR_MATCH(buf, outbuf.get(), "pre-write read");
 
   rv = sc->ResetStartupWriteTimer();
   rv = WaitForStartupTimer();
   NS_ENSURE_SUCCESS(rv, rv);
   
-  rv = sc->GetBuffer(id, &outbufPtr, &len);
+  rv = sc->GetBuffer(id, &outbuf, &len);
   NS_ENSURE_SUCCESS(rv, rv);
-  outbuf = outbufPtr;
-  NS_ENSURE_STR_MATCH(buf, outbuf, "simple write/read");
+  NS_ENSURE_STR_MATCH(buf, outbuf.get(), "simple write/read");
 
   return NS_OK;
 }
 
 nsresult
 TestWriteInvalidateRead() {
   nsresult rv;
   const char* buf = "BeardBook competitive analysis";