Examine source code of TabsUrl

{
  "manifest_version": 2,
  "name": "TabsUrl",
  "author": "Luigi Caradonna",
  "homepage_url": "https://github.com/LuigiCaradonna/TabsUrl",
  "description": "Retrieves the URLs from the open tabs, the user can save them into a text file or store them into the local storage to open them again later.",
  "version": "1.0.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "tabsurl@luigicaradonna.it"
    }
  },
  "icons": {
    "16": "icons/tabsurl-16.png",
    "32": "icons/tabsurl-32.png",
    "48": "icons/tabsurl-48.png",
    "64": "icons/tabsurl-64.png",
    "96": "icons/tabsurl-96.png",
    "128": "icons/tabsurl-128.png"
  },
  "web_accessible_resources": [
    "icons/git-logo.png"
  ],
  "browser_action": {
    "default_icon": "icons/tabsurl-32.png",
    "default_title": "TabsUrl"
  },
  "background": {
    "scripts": [
      "bg.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "cs.js",
        "overlay.js",
        "modal.js",
        "table.js",
        "save_text.js",
        "manage_storage.js"
      ],
      "css": [
        "cs.css"
      ]
    }
  ],
  "permissions": [
    "tabs",
    "storage",
    "<all_urls>"
  ]
}