Examine source code of Copy On Select

{
  "name": "Copy On Select",
  "description": "A productivity tool which copies selected text to the clipboard automatically.",
  "version": "1.1resigned1",
  "icons": {
    "128": "copy-on-select-128.png"
  },
  "permissions": [
    "tabs",
    "http://*/*",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "copy-on-select.js"
      ],
      "run_at": "document_end"
    }
  ],
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "copy-on-select@spyrosoft.com"
    }
  }
}