Mozilla kicked off its long-under-development plan to run ads in Firefox with the launch of version 33.1 on Monday.
The ads, which Mozilla calls "sponsored tiles," were first discussed by the company in February. In the months that followed, Mozilla defended the in-browser ad project against critics who called it a betrayal of the organization's philosophy, saying it was important to find other revenue sources besides its long-standing deals with search providers like Google.
Firefox 33.1, the special 10th anniversary edition released Monday, included the first instances of sponsored tiles. It followed the August introduction of the ads in Firefox's "Nightly" build, which is analogous to a pre-alpha edition.
Among the initial advertisers in the new tab page were CVS Health, the company that operates the CVS chain of drug stores, and Booking.com, a travel and accommodation site that's part of Priceline.
Sponsored tiles will occupy one or more of the thumbnails that appear in the Firefox new tab page -- the number of thumbnails depends on the size of the browser window, but appears to max out at 15 -- which historically has displayed a user's most-frequently-accessed websites.
Mozilla's original ad pitch said that only new Firefox users would see the sponsored tiles, a way to fill some of the spots that had not yet been populated with websites. Long-time Firefox users were to see only their most-frequently-visited sites.
That's not quite how it now works.
"A separate feature, Enhanced Tiles, will improve upon the existing new tab page experience for users who already have a history in their browser," Darren Herman, Mozilla's vice president of content services -- a relatively new position in the organization -- said in a blog post today.
Veteran Firefox users will be able to switch off the Enhanced mode from the new page tab if they want.
The sponsored tiles are an attempt by Mozilla to diversify its revenue sources. Currently, Mozilla books the vast majority of its income from deals with several search engines, notably Google's, that make them the Firefox default. In 2012, the last year for which Mozilla has released financial figures, revenue from its contract with Google accounted for 88% of its $311 million income. Royalty payments from all of Mozilla's search deals represented 98% of 2012's revenue.
The Google contract expires before the end of the year. Mozilla has acknowledged it's talking, but not with whom or for how much. "Mozilla is currently in the midst of negotiations," a company spokesman said Monday.
Harmon promised that Mozilla would not collect the kind of user data that most ad networks vacuum up. "Running sponsored content in Tiles is results-based, not surveillance-based," Harmon said. "We do not allow tracking beacons or code in Tiles."
By "results-based," Harmon meant that Mozilla will tell advertisers how many times their tile was clicked.
Harmon also said that the current version of the new tab page ads might not resemble those of the future. "We believe that we can do this, and offer a better way to deliver and to receive adverts that users find useful and relevant," Harmen added.
Firefox 33.1 for Windows, OS X and Linux can be downloaded from Mozilla's website. Users of the browser's stable channel build will receive the update automatically.