Firefox typically fills a new tab with tiles of your most-visited websites, but if you're one of the brave souls using the Nightly experimental build, you'll see something else in there, too: ads. Mozilla has started rolling out sponsored tiles interspersed among websites you've visited on Nightly, months after the organization first announced its plans to do. When you first launch the browser, you'll get a pop-up notification that says some of the tiles will feature sponsored content, and that it'll clearly mark which ones are ads. But TheNextWeb, which has spotted this latest change on the browser's least stable build, noticed that some ads weren't marked at all.