Introduction
Open Safari. From your Mac's menu bar, click Safari > Preferences. Click Websites > Pop-up Windows. Set your preferences.
Instructions
1) Open Safari.
2) In your Mac's menu bar, click the Safari menu option and choose Preferences.
2) Click the Websites tab. In the left-hand pane, click Pop-up Windows.
3) Use the drop-down fields to set your desired preferences.
4) Close the Safari preferences window.
Outcome
Pop-ups in Safari will behave according to the preferences that you chose.