Mozilla

The Firefox browser, lagging its well-heeled rivals, will soon be serving up an array of ads to one and all.

Mozilla, the nonprofit group that develops and updates the popular Internet browser, said Thursday that it will begin placing ads where thumbnails of your frequently visited websites would normally be found when you open a new tab. While many of those thumbnails, which Firefox calls "Enhanced Tiles," will remain as quick links to your favorite sites, some will feature sponsored logos or other promoted images.

The decision comes after a year-long experiment testing the receptivity of the ads among a small group of users.

The ads are a way for Mountain View, Calif.-based Mozilla to stay relevant at a time when more people are making use of Microsoft's Internet Explorer and Google's Chrome when browsing the Web. Mozilla hopes the sponsored tiles will help influence powerful advertising groups while not compromising its nonprofit values. The ads also represent a potential new revenue stream for Mozilla, which gets most of its funding from Google through a deal in which it is the default search engine.

"We see this as a meaningful contributor to Mozilla's revenue," Darren Herman, vice president of content services for Mozilla and the man behind the tile ads, said in an interview. "We're using ourselves to demonstrate that it's possible to advertise at a scale nobody else can."

The initiative comes as Firefox continues to lose ground to its rivals. According to Net Applications, which measures individual users' daily Internet activity, IE is the top PC browser, with a 58 percent share, followed by Chrome at 21 percent and Firefox at 14 percent.

Mozilla plans to ramp up the ads over time, but even once that's in full swing, Herman said Mozilla will tread carefully with how it places those ads.

"We are only collecting minimal viable data" related to sponsored tiles, Herman said. Mozilla will collect a user's location but no more specific than the country the user is from, how many impressions the tile received, and how many times users pinned the tile to their New Tab page or removed it.

Among the first ads shown will be anti-tobacco messages and promotions for the new Edward Snowden biopic, "Citizenfour."

The ads shown to Firefox users will depend on how long the person has been using the browser. New users will be shown sponsored tiles for Mozilla sites and Mozilla's partners.

People who've used Firefox for longer than a month will be shown sponsored tiles based on browsing history. Those tiles could be customized screenshots or logos determined by the advertiser.

Firefox will provide users an option to disable the ads, by going into the gear icon in the upper right corner of the New Tab page, and clicking away from "Enhanced." The company said that the choice to bar ads won't affect the browsing experience.