1. A method comprising: using a server computer in a media content delivery system, sending, to a plurality of browsers of client computers, one or more ordered sets of titles from a library of titles, each ordered set of titles including a particular title at a particular location in the ordered set; using the server computer, receiving, from one or more browsers of the plurality of browsers of client computers, particular data indicating impressions of the particular title and interactions with the particular title that resulted from the impressions of the particular title, in which the impressions have been automatically recorded in response to: an affirmative input from browsing over the particular title of a respective ordered set of titles, of the sent one or more ordered sets of titles, in a corresponding browser of the one or more browsers of the plurality of browsers of client computers, wherein the affirmative input from browsing over the particular title includes at least a user input indicating hovering over the particular title or a user input of scrolling over the particular title, or displaying the particular title as part of displaying initial titles of the respective ordered set of titles, of the sent one or more ordered sets of titles, in the corresponding browser of the one or more browsers of the plurality of browsers of client computers; based on the particular data, determining a location of the particular title in a particular ordered set of titles, of the library of titles, to display in a browser of a client computer system; wherein the method is performed by one or more computing devices.