• Depends.

    • could be because you had it open last time you were logged in and you have the setting to re-open windows when you log back in
    • could be because you have it set to launch on startup

    Go to Users & Groups, click you and click login items. If safari is in the box, highlight it and click the minus button at the bottom.

    If it's not there, it's because of the first thing.

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