Hi Group,
For some reason, this direct download link for the Mozilla scripts is buried deep within pages.
Try this direct link which I found and it works and has the proper extension to immediately launch NVDA's add-on manager.
https://github.com/javidominguez/MozillaScripts/releases/download/1.4/MozillaScripts-1.4.nvda-addon Clickon the link labeled:
On 12/6/2017 10:11 AM, Rob Hudson wrote:

Gene <gsasner@ripco.com> wrote:

Is there a way to download the add on already complete as the Drop Box link was?  The Drop Box link was useable in the standard way.

There might be, but I did not investigate the linked page thoroughly enough to find it. I have seen this before so I knew what to do when I got the
"xxx-master.zip"
file. All you need to do is a little file manipulation and you have it installed.