--- a/mailnews/base/util/nsMsgProtocol.cpp
+++ b/mailnews/base/util/nsMsgProtocol.cpp
@@ -187,17 +187,17 @@ nsresult nsMsgProtocol::GetFileFromURL(n
 
   nsCOMPtr<nsIFileURL>    fileURL = do_QueryInterface(uri);
   if (!fileURL)   return NS_ERROR_FAILURE;
 
   return fileURL->GetFile(aResult);
   // dougt
 }
 
-nsresult nsMsgProtocol::OpenFileSocket(nsIURI * aURL, uint32_t aStartPosition, int32_t aReadCount)
+nsresult nsMsgProtocol::OpenFileSocket(nsIURI *aURL, uint64_t aStartPosition, int64_t aReadCount)
 {
   // mscott - file needs to be encoded directly into aURL. I should be able to get
   // rid of this method completely.
 
   nsresult rv = NS_OK;
   m_readCount = aReadCount;
   nsCOMPtr <nsIFile> file;
 
@@ -209,17 +209,17 @@ nsresult nsMsgProtocol::OpenFileSocket(n
   if (NS_FAILED(rv)) return rv;
 
   // create input stream transport
   nsCOMPtr<nsIStreamTransportService> sts =
       do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
   if (NS_FAILED(rv)) return rv;
 
   RefPtr<SlicedInputStream> slicedStream =
-    new SlicedInputStream(stream, uint64_t(aStartPosition), uint64_t(aReadCount));
+    new SlicedInputStream(stream, aStartPosition, uint64_t(aReadCount));
   rv = sts->CreateInputTransport(slicedStream, true,
                                  getter_AddRefs(m_transport));
 
   m_socketIsOpen = false;
   return rv;
 }
 
 nsresult nsMsgProtocol::GetTopmostMsgWindow(nsIMsgWindow **aWindow)

--- a/mailnews/base/util/nsMsgProtocol.h
+++ b/mailnews/base/util/nsMsgProtocol.h
@@ -81,17 +81,17 @@ protected:
   // aHostName must be UTF-8 encoded.
   virtual nsresult OpenNetworkSocketWithInfo(const char * aHostName,
                                              int32_t aGetPort,
                                              const char *connectionType,
                                              nsIProxyInfo *aProxyInfo,
                                              nsIInterfaceRequestor* callbacks);
   // helper routine
   nsresult GetFileFromURL(nsIURI * aURL, nsIFile **aResult);
-  virtual nsresult OpenFileSocket(nsIURI * aURL, uint32_t aStartPosition, int32_t aReadCount); // used to open a file socket connection
+  virtual nsresult OpenFileSocket(nsIURI * aURL, uint64_t aStartPosition, int64_t aReadCount); // used to open a file socket connection
 
   nsresult GetTopmostMsgWindow(nsIMsgWindow **aWindow);
 
   virtual const char* GetType() {return nullptr;}
   nsresult GetQoSBits(uint8_t *aQoSBits);
 
   // a Protocol typically overrides this method. They free any of their own connection state and then
   // they call up into the base class to free the generic connection objects
@@ -129,17 +129,17 @@ protected:
   nsCOMPtr<nsITransport>  m_transport;
   nsCOMPtr<nsIRequest>    m_request;
   nsCOMPtr<nsICancelable> m_proxyRequest;
 
   bool          m_socketIsOpen; // mscott: we should look into keeping this state in the nsSocketTransport...
                                   // I'm using it to make sure I open the socket the first time a URL is loaded into the connection
   uint32_t      m_flags; // used to store flag information
   //uint32_t  m_startPosition;
-  int32_t       m_readCount;
+  int64_t       m_readCount;
 
   nsCOMPtr<nsIFile> m_tempMsgFile;  // we currently have a hack where displaying a msg involves writing it to a temp file first
 
   // auth module for access to NTLM functions
   nsCOMPtr<nsIAuthModule> m_authModule;
 
   // the following is a catch all for nsIChannel related data
   nsCOMPtr<nsIURI>            m_originalUrl;  // the original url

--- a/mailnews/imap/src/nsImapProtocol.cpp
+++ b/mailnews/imap/src/nsImapProtocol.cpp
@@ -9651,17 +9651,17 @@ bool nsImapMockChannel::ReadFromLocalCac
       if (fileStream && NS_SUCCEEDED(rv))
       {
         // dougt - This may break the ablity to "cancel" a read from offline mail reading.
         // fileChannel->SetLoadGroup(m_loadGroup);
         RefPtr<nsImapCacheStreamListener> cacheListener = new nsImapCacheStreamListener();
         cacheListener->Init(m_channelListener, this);
 
         // create a stream pump that will async read the specified amount of data.
-        // XXX make offset/size 64-bit ints
+        // XXX make size 64-bit int
         RefPtr<SlicedInputStream> slicedStream =
           new SlicedInputStream(fileStream, uint64_t(offset), uint64_t(size));
         nsCOMPtr<nsIInputStreamPump> pump;
         rv = NS_NewInputStreamPump(getter_AddRefs(pump), slicedStream);
         if (NS_SUCCEEDED(rv))
           rv = pump->AsyncRead(cacheListener, m_channelContext);
 
         if (NS_SUCCEEDED(rv)) // ONLY if we succeeded in actually starting the read should we return

--- a/mailnews/local/src/nsMailboxProtocol.cpp
+++ b/mailnews/local/src/nsMailboxProtocol.cpp
@@ -56,17 +56,17 @@ nsMailboxProtocol::nsMailboxProtocol(nsI
 }
 
 nsMailboxProtocol::~nsMailboxProtocol()
 {
   // free our local state
   delete m_lineStreamBuffer;
 }
 
-nsresult nsMailboxProtocol::OpenMultipleMsgTransport(uint64_t offset, int32_t size)
+nsresult nsMailboxProtocol::OpenMultipleMsgTransport(uint64_t offset, int64_t size)
 {
   nsresult rv;
 
   nsCOMPtr<nsIStreamTransportService> serv =
       do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // XXX 64-bit
@@ -112,21 +112,21 @@ nsresult nsMailboxProtocol::Initialize(n
 
         rv = OpenFileSocket(aURL, 0, -1 /* read in all the bytes in the file */);
       }
       else
       {
         // we need to specify a byte range to read in so we read in JUST the message we want.
         rv = SetupMessageExtraction();
         if (NS_FAILED(rv)) return rv;
-        uint32_t aMsgSize = 0;
-        rv = m_runningUrl->GetMessageSize(&aMsgSize);
+        uint32_t msgSize = 0;
+        rv = m_runningUrl->GetMessageSize(&msgSize);
         NS_ASSERTION(NS_SUCCEEDED(rv), "oops....i messed something up");
-        SetContentLength(aMsgSize);
-        mailnewsUrl->SetMaxProgress(aMsgSize);
+        SetContentLength(msgSize);
+        mailnewsUrl->SetMaxProgress(msgSize);
 
         if (RunningMultipleMsgUrl())
         {
           // if we're running multiple msg url, we clear the event sink because the multiple
           // msg urls will handle setting the progress.
           mProgressEventSink = nullptr;
         }
 
@@ -149,32 +149,32 @@ nsresult nsMailboxProtocol::Initialize(n
               NS_ENSURE_SUCCESS(rv, rv);
               nsCOMPtr<nsISeekableStream> seekableStream(do_QueryInterface(stream, &rv));
               NS_ENSURE_SUCCESS(rv, rv);
               seekableStream->Tell(&offset);
               // create input stream transport
               nsCOMPtr<nsIStreamTransportService> sts =
                   do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
               if (NS_FAILED(rv)) return rv;
-              m_readCount = aMsgSize;
+              m_readCount = msgSize;
               // Save the stream for reuse, but only for multiple URLs.
               if (reusable && RunningMultipleMsgUrl())
                 m_multipleMsgMoveCopyStream = stream;
               else
                 reusable = false;
               RefPtr<SlicedInputStream> slicedStream =
-                new SlicedInputStream(stream, uint64_t(offset), uint64_t(aMsgSize));
+                new SlicedInputStream(stream, offset, uint64_t(msgSize));
               rv = sts->CreateInputTransport(slicedStream, !reusable,
                                              getter_AddRefs(m_transport));
 
               m_socketIsOpen = false;
             }
           }
           if (!folder) // must be a .eml file
-            rv = OpenFileSocket(aURL, 0, aMsgSize);
+            rv = OpenFileSocket(aURL, 0, int64_t(msgSize));
         }
         NS_ASSERTION(NS_SUCCEEDED(rv), "oops....i messed something up");
       }
     }
   }
 
   m_lineStreamBuffer = new nsMsgLineStreamBuffer(OUTPUT_BUFFER_SIZE, true);
 

--- a/mailnews/local/src/nsMailboxProtocol.h
+++ b/mailnews/local/src/nsMailboxProtocol.h
@@ -90,17 +90,17 @@ private:
   // multiple messages.
   nsCOMPtr<nsIInputStream> m_multipleMsgMoveCopyStream;
 
   virtual nsresult ProcessProtocolState(nsIURI * url, nsIInputStream * inputStream,
                                         uint64_t sourceOffset, uint32_t length) override;
   virtual nsresult CloseSocket() override;
 
   nsresult SetupMessageExtraction();
-  nsresult OpenMultipleMsgTransport(uint64_t offset, int32_t size);
+  nsresult OpenMultipleMsgTransport(uint64_t offset, int64_t size);
   bool RunningMultipleMsgUrl();
 
   ////////////////////////////////////////////////////////////////////////////////////////
   // Protocol Methods --> This protocol is state driven so each protocol method is
   //            designed to re-act to the current "state". I've attempted to
   //            group them together based on functionality.
   ////////////////////////////////////////////////////////////////////////////////////////