Examine source code of devtools Extension

{
  "description": "Adds a new panel to the developer tools. The panel contains buttons that demonstrate various basic features of the devtools API.",
  "manifest_version": 2,
  "name": "devtools Extension",
  "version": "1.0.3",
  "author": "Christophe Villeneuve",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/devtools-panels",
  "icons": {
    "48": "icons/star.png"
  },
  "background": {
    "scripts": [
      "background_scripts/background.js"
    ]
  },
  "permissions": [
    "<all_urls>"
  ],
  "devtools_page": "devtools/devtools-page.html",
  "browser_specific_settings": {
    "gecko": {
      "id": "{e2bd3a5e-f6cf-41d8-a217-7224fb911533}"
    }
  }
}