--- a/netwerk/base/nsProtocolProxyService.cpp
+++ b/netwerk/base/nsProtocolProxyService.cpp
@@ -1970,16 +1970,24 @@ nsProtocolProxyService::Resolve_Internal
         nsAutoCString scheme;
         int32_t port = -1;
 
         uri->GetAsciiSpec(spec);
         uri->GetAsciiHost(host);
         uri->GetScheme(scheme);
         uri->GetPort(&port);
 
+        if (flags & RESOLVE_PREFER_SOCKS_PROXY) {
+            LOG(("Ignoring RESOLVE_PREFER_SOCKS_PROXY for system proxy setting\n"));
+        } else if (flags & RESOLVE_PREFER_HTTPS_PROXY) {
+            scheme.AssignLiteral("https");
+        } else if (flags & RESOLVE_IGNORE_URI_SCHEME) {
+            scheme.AssignLiteral("http");
+        }
+
         // now try the system proxy settings for this particular url
         if (NS_SUCCEEDED(mSystemProxySettings->
                          GetProxyForURI(spec, scheme, host, port,
                                         pacString))) {
             ProcessPACString(pacString, 0, result);
             return NS_OK;
         }
     }