"Pretty much anytime we talk about revenue at Mozilla people get suspicious," she said. "Mozillians get suspicious, and our supporters get suspicious. There's some value in that, as it reinforces our commitment to user experience and providing value to our users."

But she argued the obvious point that money is necessary to fund the foundation, and thus, Firefox and the group's other projects. And she said that money could be raised without damaging the organization's stance on user privacy or harming its reputation with its users.

The chairwoman of Mozilla Foundation, the non-profit that funds the development of Firefox, last week defended the decision to pursue in-browser ads, saying that it's important to generate revenue.

"To explicitly address the question of whether we care about generating revenue and sustaining Mozilla's work, the answer is yes," Mitchell Baker, former CEO of Mozilla Corp., the subsidiary responsible for Firefox, and now the chair of the parent foundation, wrote on a blog Thursday. "In fact, many of us feel responsible to do exactly this."

Mitchell Baker
Mitchell Baker, chairwoman of Mozilla Foundation. (Image: Mozilla.)
Baker was responding to questions and concerns raised earlier in the week after Mozilla announced "Directory Tiles," an under-development Firefox feature that would display sponsored thumbnails -- advertisements -- in the New Tabs page of new users of the browser.

In her post, Baker acknowledged that Firefox users in general, and those more intimately involved with Mozilla -- employees and code contributors -- were by nature suspicious of any connection to commercial or business needs, including producing revenue.

"When we have ideas about how content might be useful to people, we look at whether there is a revenue possibility, and if that would annoy people or bring something potentially useful," Baker said. "Ads in search turn out to be useful."

The concept of Directory Tiles as presented last week was straight-forward: When new users start Firefox, they will see pre-populated tiles, some of them advertisements, on the New Tab page. For long-time Firefox users, that page, which has room for nine thumbnails, shows the most-frequently-visited websites. Someone new to Firefox, of course, would see nothing. To jump-start the experience, Mozilla will fill the New Page spots.

Two or three of the nine thumbnails would be devoted to such ads, Baker said, and under normal circumstances, they would disappear within 30 days as the new user browsed the Web enough for Firefox to replace those ads with the user's most visited URLs.

Other Mozilla executives joined Baker in promoting the Directory Tiles idea or in providing more detail about how the ad program would work. Darren Herman, a former advertising executive and venture capitalist hired by Mozilla last year to lead a new content services group specifically tasked to find new sources of revenue, contributed an FAQ that outlined the parameters of Directory Tiles. There, Herman pointed out, as did Baker, that the ads would be served without relying on any tracking of a user's movements through the Internet. Instead, the ads would only examine the user's physical location to, for example, provide ads pertinent to that locale or in its language.

Denelle Dixon-Thayer, Mozilla's vice president of business and legal affairs, also weighed in, using a separate blog Thursday to explain why Mozilla is looking for other sources of revenue.

"Revenue diversification isn't a requirement because our search partnerships are strong and provide value to our users, to our partners and to Mozilla," Dixon-Thayer said. "Diversification is a choice for us, but just as diversity is central to a healthy Web, revenue diversity is central to a healthy project."

Mozilla actually has little diversity in its revenue stream: 88% of its 2012 revenue, the last year for which the organization has released financial information, stemmed from an agreement with Google that requires Mozilla to use Google's search engine as the default for most Firefox users.

Mozilla was paid approximately $274 million by Google in 2012, a year when the former recorded total income of $311 million.

The Google-Mozilla deal was last renewed in December 2011, when a new three-year contract was signed.

Although Dixon-Thayer argued that Mozilla's search partnerships "are strong," Mozilla's attempt to diversify revenue may indicate that the non-profit believes there's a chance that the Google deal will not be renewed this year, or that if it is, the approximately $300 million it provides annually will be reduced.

According to Web analytics company Net Applications, Firefox accounted for 18% of the world's desktop browser user share in January, down from 22% in late 2011 when it last dealt with Google. Firefox has virtually no user share of the mobile browser market.

In replies to comments appended to her blog post, Baker noted that creating Firefox OS, its browser-based mobile operating system, was "extremely expensive," and admitted that the organization had done a poor job in originally presenting the Directory Tiles concept to its user community.

But some of those who left comments for Baker were unconvinced that inserting ads into Firefox, even in the limited way Mozilla proposed, is a good idea. "You're perhaps entering onto a slippery slope where eventually 'monetization' will be the primary goal in deciding elements of the browser's design rather than user experience," warned Dan Tobias.

Others suggested that that the feature be strictly opt-in, or at the least easily disabled.

Mozilla is one of the smallest organizations that creates and maintains a browser. Of the five major developers -- Apple, Google, Microsoft, Mozilla and Opera Software -- only the last had less revenue in 2012 -- $216 million -- than Mozilla.