Page Load Time add-on in Tor Browser Bundle not working

Question

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?

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) {
    reportTiming();
  }
}, false);
if (performance && performance.timing && performance.timing.loadEventEnd > 0) {
  reportTiming();
}

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.