Examine source code of Comfortable Tabs

{
  "name": "Comfortable Tabs",
  "version": "1.0.17",
  "manifest_version": 2,
  "description": "Open a link in a new tab if and only if you double-click it",
  "icons": {
    "16": "icons/icon16.jpg",
    "48": "icons/icon48.jpg",
    "128": "icons/icon128.jpg"
  },
  "content_scripts": [
    {
      "all_frames": true,
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3c95fe85-a0dd-4a63-9309-d741ec1c4c18}"
    }
  }
}