The image was found over on Google+, and users are giving mixed reactions to the news already, with one side of the argument saying "You guys are a bunch of spoiled brats. It's a free browser for goodness sake!" and the other simply responding "Firefox 8 doesn't have ads." Perhaps Google has finally realized they could cash in on some of that large new market share?
It's not clear what platform the browser was on (it almost looks like it's on a Chromebook itself) and we weren't able to reproduce the behavior ourselves. Despite this, multiple users on the Google+ post reported that they were seeing the ads in their browsers too. We've also heard it's happening on Windows 7 based machines too.