1. A computer-implemented method comprising: receiving from a web browser, by a server system via a network, an indication of dragging, by a user of the web browser, of an element displayed on a webpage displayed by the web browser, and dropping, by the user, of the element into a content area displayed on the webpage, the element selected from the group consisting of: a first content item displayed at a location on the webpage other than in the content area, and a graphical element displayed in association with the first content item; and responsively to the indication, causing, by the server system, the web browser to display, in the content area, at least a portion of a set of one or more second content items related to the first content item.