diff --git a/mozilla/xpinstall/src/nsXPInstallManager.cpp b/mozilla/xpinstall/src/nsXPInstallManager.cpp
index f0843a1998a..cf3090d21aa 100644
--- a/mozilla/xpinstall/src/nsXPInstallManager.cpp
+++ b/mozilla/xpinstall/src/nsXPInstallManager.cpp
@@ -955,6 +955,18 @@ nsXPInstallManager::OnStartRequest(nsIRequest* request, nsISupports *ctxt)
 {
     nsresult rv = NS_ERROR_FAILURE;
 
+    // If we are dealing with a HTTP request, then treat HTTP error pages as
+    // download failures.
+    nsCOMPtr<nsIHttpChannel> httpChan = do_QueryInterface(request);
+    if (httpChan) {
+        PRBool succeeded;
+        if (NS_SUCCEEDED(httpChan->GetRequestSucceeded(&succeeded)) && !succeeded) {
+            // HTTP response is not a 2xx!
+            request->Cancel(NS_BINDING_ABORTED);
+            return NS_OK;
+        }
+    }
+
     NS_ASSERTION( mItem && mItem->mFile, "XPIMgr::OnStartRequest bad state");
     if ( mItem && mItem->mFile )
     {
@@ -963,7 +975,7 @@ nsXPInstallManager::OnStartRequest(nsIRequest* request, nsISupports *ctxt)
         rv = NS_NewLocalFileOutputStream(getter_AddRefs(mItem->mOutStream),
                                          mItem->mFile,
                                          PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE,
-                                         0664);
+                                         0600);
     }
     return rv;
 }