Ask HN: Why do Facebook and Instagram links destroy history with window.close()?

I started noticing this and thought I must be going crazy, but now anytime you follow a link to facebook or instagram (for instance, social media icons on business' websites), firefox will navigate to the link, then open a new tab while closing the old one.

Chrome avoids this, and if I try typing close() in the inspector I get a message "Scripts may close only the windows that were opened by it." which sounds like a good security feature so someone's scripts don't go closing my tabs and disappearing my back-button/history with it!

Of course I can CTRL-SHIFT-T to open the recently destroyed tab. Is this some kind of bug or does this serve a purpose?