Online advertising is more than just annoying. It can also violate users’ privacy through tracking technology meant to help target ads and measure response. Users have long had a range of tools at their disposal to combat aggressive or nosey ad-tech. But these tools often require users to install new software or poke around in their browser's settings. Today, Mozilla, the company behind the popular Firefox browser, said it will take more aggressive measures to protect users' privacy.

Future versions of Firefox will automatically block tracking codes placed by so-called third parties, advertisers or other firms that are not the website publisher; users won’t need to take any additional action. The feature is already being tested and is expected to be included in Firefox later this year. It will also block trackers that take too long to load. The features aren't designed to block ads, but may prevent some from being displayed, because the ads include tracking scripts that take too long to load.

Firefox already allows users to block tracking altogether, but the feature isn't switched on by default unless you open a "Private Browsing" session. The new features are more granular and switched on by default. They’re part of a recent push by Mozilla to emphasize privacy, including its Focus software that blocks trackers in iOS.

Mozilla isn't the first browser maker to offer protection against tracking by default. Apple's Safari browser also blocks third-party trackers. But unlike Safari, the test version of Firefox includes the block against slow-loading trackers, which currently prevents ads from appearing on Wired.com and other pages.

The features are similar to those offered by plug-ins such as Disconnect or Privacy Badger. In fact, Mozilla relies on a list of trackers created by the Disconnect team. "However, the majority of browser users do not install such add-ons, leaving them vulnerable," says Firefox product lead Peter Dolanjski, citing Mozilla's own research on user behavior. "By enabling these features by default, we can protect many more users."

Mozilla is considering additional measures against annoying ads. Firefox and other browsers have long blocked "pop-up" ads that open new windows. But now a newer form of pop-ups that appear over web content without opening a new window or tab have become popular. Dolanjski says Mozilla is researching whether it’s possible to block these “modal” pop-ups, though the company hasn’t committed to actually blocking them, if it proves feasible. Users who want to help Mozilla with this research can install a plug-in for reporting this newer type of pop-up.

Mozilla's approach is more aggressive than the ad-blocking now baked into Google's Chrome browser, which only blocks ads on pages that engage in particularly obnoxious advertising and isn't focused on protecting privacy. Microsoft recently began bundling Adblock Plus with mobile versions of its Edge browser, but it's not enabled by default.

While the approaches vary, there's a clear trend towards browsers taking a more active role in shaping the content users view. For years, browsers simply displayed content the way web publishers specified, and ran whatever code was bundled with those pages. That permissiveness led to a worse web, one plagued by video that plays automatically, ads that stalk you across the web or spread malware, and pages that are bigger than the original Doom videogame. The innovations now trickling out from browser makers have the potential to reshape the web, but also put more control into the hands of big companies like Apple, Google, and Microsoft, which make many of the most popular browsers. Mozilla represents an alternative to these massive companies.

Firefox will be the most widely used browser to block trackers by default, but it still trails Google’s Chrome in usage by a wide margin. According to Statcounter, Chrome has a nearly 60 percent share of the global browser market, while Firefox has 5 percent. Safari has about 14 percent. Statcounter's rankings didn't break out statistics for the privacy-centric browser from Brave, a company founded by former Mozilla CTO Brendan Eich.

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