Examine source code of Rainbow Fox

{
  "manifest_version": 2,
  "name": "Rainbow Fox",
  "description": "Change window color in Firefox",
  "version": "0.9.6",
  "icons": {
    "48": "src/icons/icon-48.png"
  },
  "browser_action": {
    "default_title": "Index",
    "default_popup": "/index.html"
  },
  "permissions": [
    "theme",
    "sessions"
  ],
  "background": {
    "scripts": [
      "assets/index.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "ssss@example.com",
      "strict_min_version": "58.0"
    }
  }
}