If you hold Left or Right Alt when you hit enter, it will open up in a new tab. Unless you are already in a new tab.

Simple enough! Thanks!

• • • Actually, @jscher2000 has a better answer. (I just don't know how to change the chosen solution.)

Hello LeeU,

Would you be so kind as to mark Toast3r's post as Chosen Solution  ? ("Solved the problem" button to the right of that post)

Thank you in advance  !

Also, there is a new-ish setting you can change for that (if you want Firefox to do it automatically every time):

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste intab and pause while the list is filtered

(3) Double-click the browser.urlbar.openintab preference to switch the value from false to true

In case you're curious about some of the others:

• browser.search.openintab is for the classic short search bar (optional since Firefox 57)
• browser.tabs.loadBookmarksInTabs is for bookmarks you open from the menu, toolbar, or sidebar