Examine source code of Fire Resizer

{
  "manifest_version": 2,
  "name": "Fire Resizer",
  "description": "Display and set your browser width. Excellent for responsive web design and testing media queries.  Includes keyboard shortcuts!",
  "version": "2.1",
  "browser_action": {
    "default_icon": "assets/icon_16.png",
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "assets/icon_16.png",
    "19": "assets/icon_19.png",
    "48": "assets/icon_48.png",
    "128": "assets/icon_128.png"
  },
  "permissions": [
    "storage",
    "tabs"
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "applications": {
    "gecko": {
      "id": "@fireresizer",
      "strict_min_version": "57.0"
    }
  },
  "background": {
    "scripts": [
      "js/update.js"
    ]
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Right",
        "windows": "Ctrl+Right",
        "mac": "Command+Right"
      }
    }
  }
}