I have Javascrpit for the Neko Cat and it works when you load it in a web browser. Please see below:

neko_cat.html

<script>NekoType="socks"</script>
<h1 id=nl><script src="https://webneko.net/n20171213.js"></script><a href="https://webneko.net">Neko</a></h1>

I would like to create a firefox web extension so this script is loaded on every web page.

I have looked at the following but I can't get it to work.

manifest.json

{
  "manifest_version": 2,
  "name": "Neko Cat",
  "version": "1.0",
  "description": "",
  "content_scripts": [
    {
      "matches": ["*://*.mozilla.org/*"],
      "js": ["neko_cat.js"] //code put ino a js file.
    }
  ] 
}

Any ideas on how to do this?

Thanks.