Examine source code of onion-everywhere

{
  "manifest_version": 2,
  "name": "onion-everywhere",
  "version": "0.1.2resigned1",
  "description": "Automatically redirect to onion domain if it's available.",
  "applications": {
    "gecko": {
      "id": "onion-everywhere@mozilla.org",
      "strict_min_version": "45.0"
    }
  },
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>",
    "notifications"
  ],
  "icons": {
    "48": "icons/logo-48.png",
    "256": "icons/logo-256.png"
  }
}