Examine source code of Black Sides

{
  "description": "Turn off side empty white areas on websites for more comfort",
  "manifest_version": 2,
  "name": "Black Sides",
  "version": "1.1resigned1",
  "homepage_url": "https://github.com/kjaku/blacksides",
  "icons": {
    "48": "icons/blacksides-48.png"
  },
  "applications": {
    "gecko": {
      "id": "blackSides@example.com"
    }
  },
  "permissions": [
    "activeTab",
    "storage",
    "tabs",
    "<all_urls>"
  ],
  "commands": {
    "toggle": {
      "suggested_key": {
        "default": "F9"
      },
      "description": "toggle black stripes addon on active tab site"
    },
    "wider": {
      "suggested_key": {
        "default": "F8"
      },
      "description": "wider black stripes "
    },
    "narrower": {
      "suggested_key": {
        "default": "F7"
      },
      "description": "thinner black stripes"
    }
  },
  "browser_action": {
    "default_icon": "icons/blacksides-32.png",
    "theme_icons": [
      {
        "light": "icons/blacksides-32-light.png",
        "dark": "icons/blacksides-32.png",
        "size": 32
      }
    ],
    "default_title": "Black Sides",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "back.js"
    ]
  }
}