Mozilla has revealed plans to sell advertising within Firefox’s new tabs page. Yes, this is the same Mozilla that decided to block third-party cookies by default in Firefox 22 last year – a move that was described by the Interactive Advertising Bureau’s top lobbyist as a nuclear strike on the industry.

It’s a complete change of course for the foundation but naturally, Mozilla is putting a pleasant spin on it. Darren Herman, Mozilla’s VP of content services, said the Directory Tiles will suggest pre-packaged content for first-time users. Some 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’s pursuit of their mission, he said.

In case you weren’t already aware, sponsored content is simply a fancy term for advertising.

But why the sudden change of stance on advertising? Truth be told, it likely all comes down to money. Mozilla relies on Google for a large portion of its income thanks to a $300 million per year deal to use Google as the browser’s default search engine.

That may sound like a conflict of interest considering Google has its own browser in Chrome but either way you slice it, Mozilla is making serious bank on the deal. The bad news is that the deal is up for renewal in December of this year.

With the advertising deal, Mozilla may be looking to diversify their income stream in the event a deal can’t be hammered out. As the saying goes, it’s never a good idea to put all of your eggs in one basket.