--- a/netwerk/dns/TRR.cpp
+++ b/netwerk/dns/TRR.cpp
@@ -182,17 +182,18 @@ TRR::SendHTTPRequest()
   rv = NS_NewChannel(getter_AddRefs(mChannel),
                      dnsURI,
                      nsContentUtils::GetSystemPrincipal(),
                      nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
                      nsIContentPolicy::TYPE_OTHER,
                      nullptr,   // PerformanceStorage
                      nullptr, // aLoadGroup
                      this,
-                     nsIRequest::LOAD_ANONYMOUS, ios);
+                     nsIRequest::LOAD_ANONYMOUS |
+                     (mPB ? nsIRequest::INHIBIT_CACHING: 0), ios);
   if (NS_FAILED(rv)) {
     LOG(("TRR:SendHTTPRequest: NewChannel failed!\n"));
     return rv;
   }
 
   nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(mChannel);
   if (!httpChannel) {
     return NS_ERROR_UNEXPECTED;