I have to rate to leave a comment. 5 stars, why not. Hadn't even tried it.
I just wanted to comment that you can do this by default in a single click. Middle-click opens any link in a new tab. Try middle click on the Back button.

If you hold Shift, your focus stays in the same tab. If you don't, you go to the new tab.

If you right-click (or long-click) the Back button, it shows the whole history of that tab. It's one extra click though.

Copy-paste this comment into extension description to educate people who search for this functionality. Let the extension exist.

I really like this extension but was looking for a button or a option when you hold in the back button. Having those 2 features added would make this extension perfect. Still great extension though.