The only extension that worked for me, however the native helper didn't download automatically and had to be manually installed via a link to a .dat file on the page with download instructions. The link is not visible (had to be discovered via Inspector) and the file needs to be renamed to .exe.

Auto-download doesn't work. I had to use the inspector tool on the addon pop-up webpage, download the .dat file and rename the extention to .exe I could then install the addon.

This site is awful

good

All works great!
BUT! After release Firefox 60 with support Group Policy, in our enterprise intranet we install Firefox how default web browser, and for run clickonce application we use this plugin... By group policy now we can install plugin automate... but... when this plugin install him automatically open nativeinstall.html and try to save .exe file

Can you create 2nd version of this plugin for "silent" install, e.g. plugin without html help and .dat (exe) file.
Exe file we install separattely by group policy windows.

I try to just cut off some file from xpi, and change some file for skip help files and saving exe files, but firefox don't install my new .xpi... I think because him not signatures

While this addon worked flawlessly for me, its companion app is suspicious: https://www.virustotal.com/#/file/53ac3dd47adbcf28e96ff6ba4e34af8fc7ea65bc3825df74856d36ac7b14562e/detection