Bookends Bridge reads metadata and page content from web pages you visit so it can detect bibliographic references. It sends this data only to the Bookends application running on your Mac through a local loopback connection at 127.0.0.1. The extension does not send page data, browsing activity, or personal information to Sonny Software or any remote server, and does not sell data or use it for advertising or analytics. Bookends may contact bibliographic services such as Crossref, PubMed, DataCite, Unpaywall, and DOI resolvers to resolve identifiers and locate metadata or PDFs, subject to those services’ privacy policies. Extension preferences, including its pairing token and import options, are stored locally in Firefox.