diff --git a/mozilla/mailnews/compose/src/nsMsgAttachment.cpp b/mozilla/mailnews/compose/src/nsMsgAttachment.cpp
index fece96abf37..81b3e9103f4 100644
--- a/mozilla/mailnews/compose/src/nsMsgAttachment.cpp
+++ b/mozilla/mailnews/compose/src/nsMsgAttachment.cpp
@@ -124,7 +124,7 @@ NS_IMETHODIMP nsMsgAttachment::SetContentType(const char * aContentType)
      keep only the content type alone. Therefore we need to cleanup it.
   */
   PRInt32 offset = mContentType.FindChar(';');
-  if (offset)
+  if (offset >= 0)
     mContentType.Truncate(offset);
 
   return NS_OK;
diff --git a/mozilla/mailnews/mime/src/mimemult.cpp b/mozilla/mailnews/mime/src/mimemult.cpp
index 4d61cbee188..3b7b2d13b55 100644
--- a/mozilla/mailnews/mime/src/mimemult.cpp
+++ b/mozilla/mailnews/mime/src/mimemult.cpp
@@ -456,7 +456,8 @@ MimeMultipart_create_child(MimeObject *obj)
     {
       struct mime_stream_data *msd = (struct mime_stream_data *)body->options->stream_closure;
       if (!body->options->write_html_p && body->content_type && !nsCRT::strcasecmp(body->content_type, APPLICATION_APPLEFILE))
-        msd->channel->SetContentType(APPLICATION_APPLEFILE);
+				if (msd && msd->channel)
+        	msd->channel->SetContentType(APPLICATION_APPLEFILE);
     }
 #endif
 
diff --git a/mozilla/uriloader/exthandler/mac/nsInternetConfigService.cpp b/mozilla/uriloader/exthandler/mac/nsInternetConfigService.cpp
index 68905281182..06daa9f63ed 100644
--- a/mozilla/uriloader/exthandler/mac/nsInternetConfigService.cpp
+++ b/mozilla/uriloader/exthandler/mac/nsInternetConfigService.cpp
@@ -295,8 +295,8 @@ nsresult nsInternetConfigService::FillMIMEInfoForICEntry(ICMapEntry& entry, nsIM
     
     // convert entry.extension which is a Str255 
     // don't forget to remove the '.' in front of the file extension....
-    nsCAutoString temp((char *)&entry.extension[2], (int)entry.extension[0]-1);
-    info->AppendExtension(temp.get());
+  	nsCAutoString temp((char *)&entry.extension[2], entry.extension[0] > 0 ? (int)entry.extension[0]-1 : 0);
+  	info->AppendExtension(temp.get());
     info->SetMacType(entry.fileType);
     info->SetMacCreator(entry.fileCreator);
     temp.Assign((char *) &entry.entryName[1], entry.entryName[0]);
diff --git a/mozilla/xpfe/appshell/src/nsInternetConfigService.cpp b/mozilla/xpfe/appshell/src/nsInternetConfigService.cpp
index 68905281182..06daa9f63ed 100644
--- a/mozilla/xpfe/appshell/src/nsInternetConfigService.cpp
+++ b/mozilla/xpfe/appshell/src/nsInternetConfigService.cpp
@@ -295,8 +295,8 @@ nsresult nsInternetConfigService::FillMIMEInfoForICEntry(ICMapEntry& entry, nsIM
     
     // convert entry.extension which is a Str255 
     // don't forget to remove the '.' in front of the file extension....
-    nsCAutoString temp((char *)&entry.extension[2], (int)entry.extension[0]-1);
-    info->AppendExtension(temp.get());
+  	nsCAutoString temp((char *)&entry.extension[2], entry.extension[0] > 0 ? (int)entry.extension[0]-1 : 0);
+  	info->AppendExtension(temp.get());
     info->SetMacType(entry.fileType);
     info->SetMacCreator(entry.fileCreator);
     temp.Assign((char *) &entry.entryName[1], entry.entryName[0]);