YOUTUBE SCRIPTS.  ALTERNATIVES TO USERSCRIPTS.ORG
http://www.dynamicdrive.com/
http://www.hotscripts.com/
http://www.resourceindex.com/
Scripts to use in lieu of userscripts.org, for it looks like their site is down.  http://www.isitdownrightnow.com/userscripts.org.html

Hello and thank you.

I am trying to add a download button to YouTube videos that I visit and want to use in projects.  Am not familiar with your site at all and would like some step-by-step help in completing this.  I used

https://forum.openoffice.org/en/forum/viewtopic.php?f=71&t=19268

To add a download button to your YouTube videos, just add this add-on to Firefox:
https://addons.mozilla.org/en-US/firefox/addon/download-youtube/