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Firefox now blocks ads and trackers in Private Browsing mode

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The latest version of Firefox will come with a powerful ad-blocking feature, Mozilla announced today. Under the browser's new setup, Private Browsing mode will block any script that could be used to identify a user, including ads, analytic trackers, and features like the Facebook Like button that can be tied back to social networks. The result is a more anonymous kind of browsing that will load pages faster and cut off many of the web's most surveillance-friendly features, along with the advertising networks many websites use to make money.

Previously, Private Browsing had only managed locally stored content, deleting cookies but allowing third-party scripts to run as intended by the site. Chrome's Incognito Mode takes a similar approach, clearing browser history but not interfering with any content loaded within the browser. That ensures that all the content on a given page will load and spares developers from choosing which scripts to block, but it leaves third-party tracking scripts relatively unaffected.

"We don't think you'll mind."

In the announcement, Mozilla emphasizes tracking scripts rather than advertising units, but Private Browsing mode will also function as an ad-blocker, allowing sites to load faster without serving any ads or analytics data back to the host. "You might notice that some web pages load more quickly with tracking protection," says Mozilla's VP Nick Nguyen in the video. "We don't think you'll mind."

Web tracking has become a controversial issue in recent months, after changes in iOS 9 allowed for similar functions on iPhone apps. That shift has allowed for a number of wildly successful ad-blocking apps, as well as new concerns over the ability of independent publications to survive on the open web.