1Password uses an agent to communicate between the Mac App and Safari Extension. An agent is most likely a small server process that can receive RESTful calls from extensions. This mechanism allows you to synchronize between all the various extensions (Safari, Chrome, Firefox, etc.), the Client and the main database.
The Safari extension is no longer installed directly by 1Password. Instead, you are directed to a web page containing the download of Safari extensions, thereby making the application environment convenient.
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