Examine source code of R-Element

{
  "name": "R-Element",
  "description": "Adds a context menu item that shows a panel upon click, from where you can choose to remove the clicked element.",
  "version": "2.1",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "page_action": {
    "default_popup": "popup.html"
  },
  "permissions": [
    "menus",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e810154d-95aa-46da-8c09-84442711a727}"
    }
  }
}