Use Tabs preferences in Safari to choose how pages, links, and tabs work in Safari windows. To view these preferences, choose Safari > Preferences, then click Tabs.
Open pages in tabs instead of windows
Choose one of the following:
⌘-click opens a link in a new tab
Change what the listed shortcuts for opening links do.
When a new tab or window opens, make it active
New tabs or windows open in front of the one you’re currently viewing.
Use ⌘-1 through ⌘-9 to switch tabs
Use keyboard shortcuts to select one of the first nine tabs in the tab bar.