The future of ads and privacy | The Mozilla Blog
4 min read
fairly easy
The modern web is funded by advertisements. Advertisements pay for all those "free" services you love, as well as many of the products you use on a dai
ly basis — including Firefox. There's nothing inherently wrong with advertising: Mozilla's Principle #9 states that "Commercial involvement in the development of the internet brings many benefits." However, that principle goes on to say that "a balance between commercial profit and public benefit is critical" and that's where things have gone wrong: advertising on the web in many situations is powered by ubiquitous tracking of people's activity on the web in a way that is deeply harmful to users and to the web as a whole.

Some Background

The ad tech ecosystem is incredibly complicated, but at its heart, the way that web advertising works is fairly simple. As you browse the web, trackers (mostly, but not exclusively advertisers), follow you around and build up a profile of your browsing history. Then, when you go to a site which wants to show you an ad, that browsing history is used to decide which of the potential ads you might see you actually get shown.

The visible part of web tracking is creepy enough — why are those pants I looked at last week following me around the Internet? — but the invisible part is even worse: hundreds of companies you've never heard of follow you around as you browse and then use your data for their own purposes or sell it to other companies you've also never heard of.

The primary technical mechanism used by trackers is what's called "third party cookies". A good description of third party cookies can be found here, a cookie is a piece of data that a website stores on your browser and can retrieve later. A third party cookie is a cookie which is set by someone other than the page you're visiting (typically a tracker). The tracker works with the web site to embed some code from the tracker on their page (often this code is also responsible for showing ads) and that code sets a cookie for the tracker. Every time you go to a page the tracker is embedded on, it sees the same cookie and can use that to link up all the…
Eric Rescorla
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