Mozilla on Friday said it would chuck its plan to advertise within Firefox, explaining that the money-making strategy "isn't the right business for us at this time."

The turn-about suspends, if not ends, a two-year project to expand the open-source browser's revenue stream beyond the one it has relied on for years: contracts with search providers.

"We have ... made the decision to stop advertising in Firefox through the Tiles experiment in order to focus on content discovery," wrote Darren Herman, Mozilla's vice president of content services, in a post to a Mozilla blog Friday. Herman, a former advertising executive and venture capitalist, joined Mozilla in 2013 to kick-start the in-browser ad project.

"Advertising in Firefox could be a great business, but it isn't the right business for us at this time because we want to focus on core experiences for our users," Herman continued. "We want to reimagine content experiences and content discovery in our products."

However, Herman didn't permanently shut Firefox's advertising door. "Mozilla will continue to explore ways to bring a better balance to the advertising ecosystem for everyone's benefit, and to build successful products that respect user privacy and deliver experiences based upon transparency, choice and control," he said.

If Mozilla does at some point return to the in-browser ad idea, it will be without Herman: On Friday, he announced he is leaving Mozilla at the end of the month.

Mozilla first broached the idea of running ads in Firefox in February 2014 when it launched the "Directory Tiles" concept. The idea then was straight-forward: When new users started Firefox, they would see pre-populated tiles, some of them "sponsored" -- in effect advertisements -- on the New Tab page. For long-time Firefox users, that page would continue to show the most-frequently-visited websites.

When it revealed the Tiles idea, Mozilla acknowledged that it was looking for ways to expand revenue, which historically had been overwhelmingly from search providers, and until late 2014, almost exclusively from Google.

By November, 2014, "sponsored" tiles -- in English, advertisements -- were appearing in Firefox. At that time, Mozilla also revealed that it would also show ads -- although it called them "Enhanced Tiles" at the time -- to long-time Firefox users as well as newcomers.

That came about in May 2015, when Mozilla rebranded the ad push as "Suggested Tiles," and announced advertisements would begin appearing in all Firefox users' browsers by the summer. "We want to show the world that it is possible to do relevant advertising and content recommendations while still respecting users' privacy and giving them control over their data," Herman said at the time.

Initially, Herman added, users would see advertisements for "Mozilla causes and Firefox products," but later the slots were to be filled by advertisers' wares.

On Friday in the latest version of Firefox, Computerworld saw just one tile with the "sponsored" label on the browser's New Tab display. The tile led to BarkBox, a website that sells dog treats and toys.

According to Herman on Friday, Mozilla will "wind down this experiment over the next few months."

While the idea of running ads in Firefox was not necessarily counter to its professed mission of "a better Internet," it ran up against the expectations of many users, who had gravitated to -- and stuck with -- Firefox because it was the biggest alternative to browsers built by major tech companies, like Apple, Google and Microsoft, all of whom -- Google in particular -- make money on ads.

The decision to scrap the Tiles project may have been due to pushback from users, from within the Mozilla volunteer community -- which Mozilla relies heavily on -- from a lack of interest on the part of advertisers, or a combination of all of the above.

Firefox may not have been an attractive platform for large-scale advertisers because its share of the browser market has been dwindling. Ironically, Firefox's user share -- a proxy for the percentage of the world's PC owners who use it to reach the Web -- jumped in November. According to metrics vendor Net Applications, Firefox's user share climbed by almost a full percentage point last month to 12.2%, erasing almost all of the losses it sustained over the previous 12 months.

Mozilla's browser still lags far behind Microsoft's Internet Explorer and Google's Chrome, however, which in November posted user shares of 50% and 31.4%, respectively.