Examine source code of Bookmark it!

{
  "manifest_version": 2,
  "name": "Bookmark it!",
  "version": "1.1",
  "description": "A simple bookmark button",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/bookmark-it",
  "icons": {
    "48": "icons/bookmark-it.png",
    "96": "icons/bookmark-it@2x.png"
  },
  "permissions": [
    "bookmarks",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/star-empty-38.png",
    "default_title": "Bookmark it!"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cc9c0295-9177-40f3-99e6-07652e363c9f}"
    }
  }
}