I've just configured Tor Browser Bundle as a normal browser (that is directing the traffic over the normal internet route rather than the Tor network) by following these (and these) instructions. This is just for some measurements I need to do, and I am not going to use this for normal browsing so anonymity is not a concern over here.

So, basically, what I want to do is to measure the page load time of a website loaded on this modified Tor browser. I was using this add-on in Firefox (52.0.2) previously but it ceases to work in Tor. I was wondering, are there any configurations (for example in about:config) that Tor has that prevent this add-on from working?

1 Answer 1


Yes, Tor Browser disables a lot of performance timing options since they can be used in side-channel and fingerprinting attacks from javascript on webpages.

The extension code does this

function reportTiming() {
  self.port.emit('timing', JSON.stringify(performance.timing));
window.addEventListener('load', function() {
  if (performance && performance.timing) {
}, false);
if (performance && performance.timing && performance.timing.loadEventEnd > 0) {

But since performance.timing.loadEventEnd > 0 will never be true, it'll never report the page load end timing and so won't get a diff to measure from.

There are a few about:config setting you may want to look at: dom.enable_user_timing, dom.enable_resource_timing and dom.enable_performance.

  • Thanks for your response! I looked into these and just set them as true but that doesn't seem to have any effect for some reason.
    – QPTR
    Apr 8, 2017 at 7:05
  • Strange, it works for me. Enabled those 3 settings and reloaded the page with the addon installed and it gave me results?
    – cacahuatl
    Apr 8, 2017 at 16:39
  • It works now. I think the problem was that dom.enable_performance parameter seems to reset itself when I close the browser. It works when I enable it again. Any ideas on why it resets?
    – QPTR
    Apr 8, 2017 at 17:17

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