Facebook is trialling an ad targeting system in its users’ newsfeeds that allows marketers to modify messages to users based on their browsing history.

Until now, Facebook has used the system to target graphical display ads to the right side of its users’ page, as per websites visited in the past.

Initially, Facebook is rolling out the feature which incorporates Facebook Exchange and will allow only a few firms, including TellApart, MediaMath and Nanigans, to place ads in the news feeds of desktop users, while further firms will be added later.

The system was trialled in mid-2012: Facebook’s initial public offering led it to redouble efforts to increase its advertising revenue.

According to Facebook, the system will be initially offered for newsfeed ads that appear on desktop PCs, but not on mobile devices.

Facebook spokeswoman Elisabeth Diana said desktop is more in line with what FBX (Facebook Exchange) has been doing effectively in the right hand side. "And we also find that desktop is the place where more people convert from seeing direct-response ads," Diana said.

Facebook revealed that allowing marketers to place Facebook Exchange ads into the news feed would not increase the number of ads, while more new relevant ads for users will replace the older ones in the newsfeed.