SFNMutt User

To get the download button to show up you need to switch to the old youtube style.
The directions in this youtube video work.
Once you do that the button will showup & the video download links will work.

To get the MP3 option to work you need to edit the userscript. Scroll down to line 297 and change the line to the following.

'url': 'https://www.recordmp3.co/#/watch?v=' + encodeURIComponent(location.href),

now the MP3 option will work too.