This extension does still work, I use it on 4 computers, 3 different operating systems (Mac, Linux, Windows 10) with the latest version of Firefox (72.0.2 64-bit at the time of this reply). You might be expecting it to do something that it doesnt, the only thing it does is forces a new tab to pop out into its own window.

If it ever does stop working, rest assured I will update it, because I personally use it.