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in the toolbar (or use the on your Mac, do any of the following:Control-click a bookmark, then choose Open in New Tab from the shortcut menu.
Control-click a bookmarks folder, then choose Open in New Tabs.
Each bookmark in the folder opens in a new tab.
To open the bookmarks sidebar, click the Sidebar button 
on your Mac, choose Safari > Preferences, then click Tabs.
Click the “Open pages in tabs instead of windows” pop-up menu, then choose an option:
Never: Links designed to open in new windows open in new windows.
Automatically: Links designed to open in new windows open in new tabs.
Always: All links designed to open in new windows open in new tabs, including links designed to open in specially formatted separate windows.
Reopen a recently closed tab
In the Safari app
Close tabs in Safari on Mac