Examine source code of onions-everywhere

{
  "browser_specific_settings": {
    "gecko": {
      "id": "onions-everywhere@rany.eu.org",
      "strict_min_version": "48.0"
    }
  },
  "background": {
    "scripts": [
      "http.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://*/*"
      ],
      "run_at": "document_end",
      "js": [
        "meta.js"
      ]
    }
  ],
  "manifest_version": 2,
  "name": "onions-everywhere",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://*/*"
  ],
  "version": "1.4",
  "description": "Automatically redirect to onion domain if it's available."
}