Only sniff text/plain types if the channel says it's still text/plain (this may

be changed after the header is parsed by other components, eg ones listening to
HTTP notifications).  Bug 273306, r=biesi, sr=darin

uriloader/base/nsURILoader.cpp

@@ -288,20 +288,24 @@ NS_IMETHODIMP nsDocumentOpenInfo::OnStartRequest(nsIRequest *request, nsISupport
   if (httpChannel && mContentType.IsEmpty()) {
     // This is our initial dispatch, and this is an HTTP channel.  Check for
     // the text/plain mess.
-    nsCAutoString contentType;
+    nsCAutoString contentTypeHdr;
     httpChannel->GetResponseHeader(NS_LITERAL_CSTRING("Content-Type"),
-                                   contentType);
+                                   contentTypeHdr);
+    nsCAutoString contentType;
+    httpChannel->GetContentType(contentType);
+    
     // Make sure to do a case-sensitive exact match comparison here.  Apache
     // 1.x just sends text/plain for "unknown", while Apache 2.x sends
     // text/plain with a ISO-8859-1 charset.  Debian's Apache version, just to
     // be different, sends text/plain with iso-8859-1 charset.  Don't do
     // general case-insensitive comparison, since we really want to apply this
     // crap as rarely as we can.
-    if (contentType.EqualsLiteral("text/plain") ||
-        contentType.Equals(
+    if (contentType.EqualsLiteral("text/plain") &&
+        (contentTypeHdr.EqualsLiteral("text/plain") ||
+         contentTypeHdr.Equals(
              NS_LITERAL_CSTRING("text/plain; charset=ISO-8859-1")) ||
-        contentType.Equals(
-             NS_LITERAL_CSTRING("text/plain; charset=iso-8859-1"))) {
+         contentTypeHdr.Equals(
+             NS_LITERAL_CSTRING("text/plain; charset=iso-8859-1")))) {
       // Check whether we have content-encoding.  If we do, don't try to detect
       // the type, since that will lead to the content being automatically
       // decompressed....