Examine source code of cubicon for Salesforce

{
  "manifest_version": 2,
  "name": "cubicon-salesforce",
  "version": "1.7",
  "options_ui": {
    "page": "opts.html",
    "browser_style": true
  },
  "description": "Sets the favicon tab icon for different Salesforce orgs to different colors.",
  "permissions": [
    "storage",
    "cookies"
  ],
  "browser_action": {
    "browser_style": true,
    "default_popup": "popup.html",
    "default_icon": {
      "128": "blue-box.png"
    }
  },
  "icons": {
    "128": "blue-box.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.force.com/*",
        "https://*.salesforce.com/*"
      ],
      "js": [
        "script.js"
      ]
    }
  ]
}