Examine source code of Tally-Ho!

{
  "manifest_version": 2,
  "name": "Tally-Ho!",
  "version": "1.0",
  "description": "A simple tally counter for the browser.",
  "icons": {
    "48": "icons/icon.svg"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.mozilla.org/*"
      ],
      "js": [
        "tallyho.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icons/icon.svg",
    "default_title": "Tally-Ho!",
    "default_popup": "main.html"
  }
}