Examine source code of Feed Indicator

{
  "manifest_version": 2,
  "name": "Feed Indicator",
  "version": "0.4.4",
  "description": "Adds an icon to indicate RSS/Atom feeds to address bar and previews a feed.",
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "57.0",
      "id": "{40688d2e-e8c2-40ec-a80b-9ebd050cd50d}"
    }
  },
  "icons": {
    "48": "icon.svg"
  },
  "permissions": [
    "menus",
    "storage",
    "http://*/*",
    "https://*/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "js": [
        "inject.js"
      ],
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start"
    }
  ],
  "page_action": {
    "browser_style": true,
    "default_icon": "action.svg",
    "default_popup": "popup.html"
  },
  "commands": {
    "_execute_page_action": {}
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  }
}