Any decent web browser has some sort of incognito browsing mode that adds at least the appearance of a more private user experience. Now the folks behind the Firefox browser say their latest update includes an enhanced Private Browsing mode that limits tracking to the point of actually blocking some ads.

In a new blog post and the above video, Firefox VP Nick Nguyen explains the basics of the updated Private Browsing mode, which is available in version 42 of the browser — available for Windows, Mac, Android, and Linux.

The mode doesn’t block all ads, just ones that the browser determines are tracking the user’s online behavior. Nguyen acknowledges this may have the result of making some sites appear broken, which is why users have the ability to disable Tracking Protection for individual sites. It can also be turned on/off universally when you launch a Private Browsing window.

We tried Private Browsing on a couple of different popular sites and in both cases saw that significant ad units were blocked from showing up.

Here’s the People.com homepage without Private Browsing. Notice the large magenta “PC Does” campaign ads in the superheader and to the right of the People cover:

Here’s the same page viewed through Private Browsing. Notice those two ad units are simply gone:

A more obvious example can be seen on this story page from Bleacher Report, where the before image shows a large ad skin and ad module for Bud Light:

Those ads are completely gone when you open the same page in Private Browsing:

Ad blocking is a huge bone of contention in the war of words between advertisers (who pay for their ads to be seen), content companies (who need ad revenue to pay their bills), and privacy-minded consumers (who don’t like to be followed everywhere they go).

Estimates say that ad-blocking tech caused websites to miss out on $22 billion in ad revenue in 2014 alone. To some, viewing a free, ad-supported site without letting the ads load is tantamount to thievery. Others counter that people would not be blocking ads if they weren’t so invasive and didn’t result in slow load times.

Recently, the Interactive Advertising Bureau — a trade group representing the companies behind most of the online ads seen in the U.S. — admitted that the industry “messed up” by going too far with too many ads that did too much tracking of user behavior.

The IAB then introduced a new “LEAN” standard for ads that don’t cripple web pages and at least stop tracking people after they’ve made a purchase through an ad.

The Electronic Frontier Foundation has a Privacy Badger plugin that tries to identify and prevent trackers from ads. The plugin does not require the user to be in incognito or private mode, but like the Firefox update, it can result in broken pages, requiring users to whitelist pages or individual trackers.

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