From the analyst covering "They’ve warned about a decline in one of the basic fundamental financial drivers." which was "changes in the fourth quarter that cut the number of viral videos in people’s news feeds. Those tweaks, and others, have already reduced time spent on Facebook by roughly 50 million hours a day, he noted." I am going to assume that FB is smart enough to have figured out how to trim the 50m hour eng…
That increase more than offsets the decline in the amount of time users spent on Facebook. So it looks like the value of advertising has improved.