Facebook's newest ad format lets a marketer target shoppers who recently browsed its products with an ad encouraging them to install the merchant's mobile app.

Facebook Inc. today rolled out a new way for retailers to prod consumers to download their apps. The social network’s new dynamic ads for mobile app installs enable a retailer to target an ad at a consumer who recently browsed its products, and that ad encourages him to download the merchant’s app.

“Advertisers can also use this tool to show relevant product ads to people who are most likely to install an app,” a Facebook spokeswoman says.

The ad format builds on Facebook’s dynamic ads—the ad format that lets retailers and other advertisers serve shoppers ads based on the products they looked at on the merchant’s site or app—and dynamic ads for retail, which enable a retailer to dynamically showcase products available in a store that’s nearby the consumer seeing the ad.

The social network is rolling out the new ad unit at an interesting time when mobile traffic to many e-commerce sites is decreasing as consumers increasingly shop within mobile apps. For instance, mobile web traffic on Black Friday decreased year over year and even week over week for 20 major e-retailers, according to digital analytics firm SimilarWeb Ltd.

Facebook also rolled out view-through attribution, which enables mobile app advertisers to assign credit to ads that consumers view but don’t click on. Finding ways to help retailers better understand the value of advertising on Facebook and Instagram is important given that last-click attribution often shows social networks driving a tiny share of overall revenue. For instance, Adobe Digital Insights reports that from Nov. 1-Dec. 5, social networks drove 0.9% of retailers’ holiday sales.