You already know that too many tracking cookies will slow Web page loading down to a crawl. Now, a study by Mozilla and Columbia University quantifies the problem.
According to Columbia's Georgios Kontaxis and Mozilla's Monica Chew, spiking the excessive load of extraneous connections on the Alexa top 200 news sites can improve page load time by 44 per cent and cut data usage loading news sites by 39 per cent.
Disturbingly, they also found that 99 per cent of the top 200 news sites carried “at least one unsafe element” (as defined by the Disconnect blocklist).
The duo tested Firefox's Tracking Protection in this paper (PDF), presented to the IEEE's Web 2.0 Security & Privacy workshop.
The performance boost observed in the paper comes entirely from limiting third-party connections. As they note: “the overhead eliminated by Tracking Protection comes from reducing third-party rather than first party content on each page”.
For a concrete example, they refer to Weather.com: by eliminating the 45 additional domains the page tries to contact during loading, the page size was cut from 4.3 Mbytes to 2.8 Mbytes, and loaded in 3.5 seconds instead of 6.3 seconds.
It's not just advertising that's loading up sites, though: too many different “share this” buttons to Twitter, Facebook, video site links, and Disqus for commenting also set cookies and load up the sites.
As the researchers note, “The Internet’s principal revenue model leads to misaligned incentives between users, advertisers, and content providers, essentially creating a race to the bottom”.
It may well be that track-bloat creates its own incentive the other way: that a user, having turned on something like Tracking Protection (or AdBlock, which the researchers take a dig at for being less effective than Mozilla's approach), fall in love with the fast page loads.
Tracking Protection was introduced in Firefox 35, using an API to Google's Safe Browsing URL and the Disconnect privacy blocklist (it's enabled in about:config by setting privacy.trackingprotection.enabled to “true”). ®