It looks like they're going to be monetizing by partnering with specific retailers. From the plugin description:
> Buy Happy retail partners will soon be giving you deals to share with friends and family via social media. And we’ll be adding more powerful features to Buy Happy as well — while building a fun community along the way. Isn’t it time to add Buy Happy to your browser?
> Buy Happy retail partners will soon be giving you deals to share with friends and family via social media. And we’ll be adding more powerful features to Buy Happy as well — while building a fun community along the way. Isn’t it time to add Buy Happy to your browser?