How do I install the addon LibreNS++ in Firefox?

[Homyland]

Hello. I'm trying to access the install of LibreNS++.
But I don't find any button that installs this addon in the GitLab page.

When I tried to install Greasemonkey, page was blank (but you could see correctly the URL) and there were no pop-ups or signs of installation of Greasemonkey.

Can someone help me?

[Racoda]

Try this link:
https://gitlab.com/RunasSudo/LibreNSpp/ ... pp.user.js

Or:
Open the userscript file: https://gitlab.com/RunasSudo/LibreNSpp/ ... pp.user.js
Click "open raw" in the top right (next to Edit/Web IDE). A Greasemonkey install popup should appear.
If that fails as well, create a new script from the Greasemonkey menu, then copy and paste the contents of the userscript file (and save).

[Guillean Republic]

I want to install it on Opera, any help?