A browser executing on a client device can detect external calls to remote servers generated by an online document. The browser can detect, in external content received in response to the external calls and for presentation in the online document, metadata describing domains that contributed to the delivery of the external content to the client device. The browser can aggregate, for each of the domains, a contribution of the domain to enable the presentation of the external content with the online document over a specified time period. The browser can present a visual representation of the contribution of each of at least some of the domains. The browser can receive, in response to interaction with the visual representation, a selection of one or more domains among the at least some domains. The browser can prevent the one or more domains from receiving subsequent external calls from the browser.