UPDATED. The chairwoman of Mozilla Foundation, the non-profit that funds the development of Firefox, defended the decision to pursue in-browser ads, saying that it's important to generate revenue.\n\t"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 in a blog\u00a0post. "In fact, many of us feel responsible to do exactly this."\n\tFirefox, the open source, somewhat anti-establishment browser, is going mainstream, with a plan to put ads in front of users, the Mozilla Foundation announced this week. For now, the ads will be confined to the tabs page of new users, but if the initial rollout succeeds, I expect them to spread.\n\tPublishers will be able to purchase sponsored tiles that will appear alongside normal tiles, with a clear \u201cpromoted\u201d label, Daren Herman, the foundation's VP of content, said in a blog post.\n\tAccording to Herman, the Directory Tiles \u2013 he doesn\u2019t want to call them ads \u2013 are there to improve the experience by suggesting pre-packaged content for first-time users. \u201cSome of these tile placements will be from the Mozilla ecosystem, some will be popular websites in a given geographic location, and some will be sponsored content from hand-picked partners to help support Mozilla\u2019s pursuit of our mission,\u201d says Herman.\n\tMozilla has not yet said when Directory Tiles will start to appear.\n\tSponsored content is almost always a euphemism for ads or marketing material.\n\tAlthough Herman doesn\u2019t say why Mozilla is making the move at this time, it\u2019s not too hard to make an educated guess. Roughly 90 percent of Mozilla\u2019s revenue comes from Google, which pays the non-profit foundation for making its search engine Firefox\u2019s default. Since Firefox is losing market share, and Google has its own browser \u2013 Chrome \u2013 it seems likely that the next time the agreement is negotiated, there will be less in it for Mozilla. (I asked Mozilla to confirm this and a few other points but have not yet heard back. I\u2019ll update this post when I do.)\n\tCan a user opt out? There\u2019s no mention of that in Herman\u2019s blog. Without having seen the new page, there\u2019s no way to know how intrusive it will feel, but if it the ads are confined to the tabs page, they probably won\u2019t be any more annoying than the ads that currently follow you all over the Web.\n\tAnd speaking of ads that follow you, Mozilla made a splash last year when it chose to block third-party cookies (a favored device of advertising companies) by default and also created a do-not-track feature that makes it harder for companies to serve targeted advertising to users.\n\tGiven that history, Mozilla's decision to make nice with the advertising world is somewhat surprising, but considering the financial realities the foundation faces, it\u2019s not exactly shocking. Still, I suspect that Mozilla will get an earful from Firefox users once Directory Tiles appear. And the volume of those protests could have a significant impact on the future of the advertising initiative.