Examine source code of Upslash

{
  "name": "Upslash",
  "description": "Bookmarking reinvented for distributed teams",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "icons": {
    "16": "icons/border-16.png",
    "48": "icons/border-48.png",
    "96": "icons/border-96.png",
    "128": "icons/border-128.png"
  },
  "version": "2.2",
  "manifest_version": 2
}