Trackers Slow Down Your Browser

This is the second article in our series about trackers and internet privacy laws. Click here to start with the first article.

We recently blogged about pernicious little programs, called trackers, that are embedded in popular web pages all over the internet, gathering information about you and your browsing habits.

There have been some blogs and news stories about the legal and privacy implications surrounding trackers, but few have discussed how much these little buggers slow down your browser.

We suspected the performance hit to be measurable, but were surprised to discover that the current trackers on some popular websites can double the time it takes to load web pages, as shown below:

trackers slow down web page load times

That might be acceptable if the trackers were performing a service that you wanted or at least asked for. Instead they are slowing you down so the web sites you visit can profit even more from your eyeballs, and possibly compromise your privacy.

Testing Methodology

All of the speed tests were performed using the Firefox Web browser. We chose Firefox because of the utility plugins that are available. We have no reason to believe the result would be much different using other browsers.

We decided to compare what is called the "page load" time, with and without trackers running. That seemed to be the most meaningful measurement to people browsing the web. It is basically the time it takes to for the page to become fully functional; in other words, when all of the text and graphics on the page have appeared, all of the links are active, all of the scripts have finish executing, etc. For the non-techie, that's roughly the time it takes for the animated "page loading" icon in your browser to stop.

Blocking Trackers

In order to test page load times with a without trackers running, we installed a few browser plugins*:

  • Adblock Plus: A cross-browser plugin that blocks third party javascript and images from appearing on web pages.
  • NoScript: A Firefox plugin that lets you list which websites can execute JavaScript, Java, Flash and other plugins on the web pages you browse.
  • Ghostery: A cross browser plugin designed to evade web trackers by, in part, blocking scripts from websites you don't trust.

If you want to install these plugins for yourself and see if you can browse the web faster, click here to follow our easy installation guides*.


We used Firebug*, a handy free web development plugin, to record the "onload" time for each site. Onload time represents the time it from the first request until the "load event" fires. According to the "load event fires at the end of the document loading process. At this point, all of the objects in the document are in the DOM, and all the images and sub-frames have finished loading."

In order to generate a large enough data set, we refreshed each page 26 times with trackers running, and 26 times with trackers blocked from running. The first result from each series was discarded so we would not count how long it takes to load images, etc. into the browser's cache.

trackers slow down web page load times
trackers slow down web page load times

As you can see from the above charts, when trackers are not allowed to run, the two sites load much faster, and the load time is very consistent. When trackers are allowed to run, the load time varies quite a bit from one refresh to the next. We're not exactly sure why, but it is odd behavior. We might look into this further.

*Caution: We do not endorse or recommend any of the above plugins. They could gather and use your information or install something on your system that you don’t want. Use them at your own risk.

Thanks to Mike B., who did the testing, most of the research and contributed to this article.