--- a/dom/webbrowserpersist/nsWebBrowserPersist.cpp
+++ b/dom/webbrowserpersist/nsWebBrowserPersist.cpp
@@ -8,16 +8,17 @@
 #include "nspr.h"
 
 #include "nsIFileStreams.h"       // New Necko file streams
 #include <algorithm>
 
 #include "nsAutoPtr.h"
 #include "nsNetCID.h"
 #include "nsNetUtil.h"
+#include "nsIClassOfService.h"
 #include "nsIInterfaceRequestorUtils.h"
 #include "nsILoadContext.h"
 #include "nsIPrivateBrowsingChannel.h"
 #include "nsComponentManagerUtils.h"
 #include "nsIComponentRegistrar.h"
 #include "nsIStorageStream.h"
 #include "nsISeekableStream.h"
 #include "nsIHttpChannel.h"
@@ -1492,16 +1493,22 @@ nsresult nsWebBrowserPersist::SaveChanne
         rv = NS_NewBufferedInputStream(getter_AddRefs(bufferedInputStream),
                                        fileInputStream, BUFFERED_OUTPUT_SIZE);
         NS_ENSURE_SUCCESS(rv, rv);
         nsAutoCString contentType;
         aChannel->GetContentType(contentType);
         return StartUpload(bufferedInputStream, aFile, contentType);
     }
 
+    // Mark save channel as throttleable.
+    nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(aChannel));
+    if (cos) {
+      cos->AddClassFlags(nsIClassOfService::Throttleable);
+    }
+
     // Read from the input channel
     nsresult rv = NS_MaybeOpenChannelUsingAsyncOpen2(aChannel, this);
     if (rv == NS_ERROR_NO_CONTENT)
     {
         // Assume this is a protocol such as mailto: which does not feed out
         // data and just ignore it.
         return NS_SUCCESS_DONT_FIXUP;
     }