Examine source code of Custom CSS

{
  "manifest_version": 2,
  "applications": {
    "gecko": {
      "id": "kenny@qutebox.com"
    }
  },
  "name": "Custom CSS",
  "description": "Overwrite page CSS",
  "version": "1.1",
  "short_name": "ext-custom-css",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "default_icon": "icon16.png",
    "default_popup": "popup.html",
    "default_title": "Edit page CSS"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "myscript.js"
      ]
    }
  ],
  "permissions": [
    "tabs",
    "storage",
    "http://*/",
    "https://*/"
  ]
}