Four ways to open a new Firefox tab in the background

Sometimes while browsing the web, often you find some interesting link on a web page, right in the middle of the text which you've yet to finish reading. At such times, you want to open that link in a background tab so you can read it later and then return to the original article. For Firefox users, I would like to share four different ways to open any link in a new background tab without installing addons.