In one aspect, a content item presentation server sends, to a first client of the server, browser-executable instructions implementing a presentation application. The instructions are configured to present, at the first client, at least a portion of a content item in the presentation application with at least one user control of the presentation application for navigating the content item in a particular manner disabled. After sending the instructions, the server receives, from a second client of the server, a first command to navigate the content item in the particular manner. In response to receiving the first command, the server sends, to the first client, a second command to navigate the content item in the particular manner thereby causing the presentation application to automatically navigate, at the first client, the content item in the particular manner.