FIXED IT! The following was translated from another reviewer:
This add-on is very good!
At first I stopped using it because it seemed broken, but recently I noticed that the download button "Px Downloader" is somehow "invisible".
If you hover your mouse over where the download button should be, you will notice that the mouse pointer changes shape to hyperlink. It means that the button is present, but invisible. At least that's my case...
I hope this helps you until the problem is finally solved.