The user has two ways to fix this.
1. The main fix for this is to adjust the availability settings. Apple menu> System Preferences> Keyboard> Shortcuts Tab> Access Full Keyboard: In windows and dialogs, press Tab to move the keyboard focus between:. Select All Controls . button. This allows Safari, as well as other applications, to get focus on buttons and other user interface elements.

2. In addition, you can configure this in the advanced Safari settings, as specified in j08691 .
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