Be sure to set byte range for mailbox urls where the action is save file to disk.

mailnews/local/src/nsMailboxUrl.cpp

@@ -443,7 +443,8 @@ NS_METHOD nsMailboxUrl::SetURLInfo(URL_Struct *URL_s)
     /* Hook us up with the world. */
     m_URL_s = URL_s;
 	if (m_mailboxAction == nsMailboxActionDisplayMessage || m_mailboxAction == nsMailboxActionCopyMessage
-		|| m_mailboxAction == nsMailboxActionMoveMessage)
+		|| m_mailboxAction == nsMailboxActionMoveMessage || m_mailboxAction == 	nsMailboxActionSaveMessageToDisk 
+		|| m_mailboxAction == nsMailboxActionAppendMessageToDisk)
 	{
 		// set the byte field range for the url struct...
 		char * byteRange = PR_smprintf("bytes=%d-%d", m_messageKey, m_messageKey+m_messageSize - 1);