Examine source code of MentiPlus

{
  "manifest_version": 2,
  "name": "MentiPlus",
  "version": "4.9",
  "description": "Mentimeter formatting extension. Change a graph column's colour or the format of the axis text using a contextual menu",
  "browser_specific_settings": {
    "gecko": {
      "id": "mentiPlus@example.com",
      "strict_min_version": "58.0"
    }
  },
  "icons": {
    "32": "icon_32.png",
    "48": "icon_48.png",
    "128": "icon_128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_ui": {
    "page": "options.html"
  },
  "content_scripts": [
    {
      "css": [
        "styles.css"
      ],
      "js": [
        "jquery.js",
        "manual.js",
        "content.js"
      ],
      "matches": [
        "https://www.mentimeter.com/app/*"
      ]
    }
  ],
  "permissions": [
    "storage"
  ],
  "web_accessible_resources": [
    "scales_1.png",
    "scales_2.png",
    "dots.png",
    "menu_1.png",
    "menu_2.png",
    "mt1.png",
    "mt2.png",
    "mt3.png",
    "mt4.png",
    "mt5.png",
    "mt6.png",
    "disable.png",
    "opts_0.png",
    "opts_1.png",
    "opts_2.png",
    "opts_3.png",
    "opts_4.png",
    "options.html",
    "icon.jpeg",
    "manual.js",
    "focusFrame.png",
    "focusFrame_2.png",
    "disableMenuItem.png",
    "disableDemo.png",
    "mentImage.png"
  ]
}