Examine source code of OpenDownload3

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "default_locale": "en",
  "description": "__MSG_extensionDescription__",
  "version": "0.0.7",
  "homepage_url": "https://github.com/jmlag/OpenDownload3",
  "browser_specific_settings": {
    "gecko": {
      "id": "@opendownload3",
      "strict_min_version": "59.0a1"
    }
  },
  "icons": {
    "48": "icon-48.png"
  },
  "permissions": [
    "<all_urls>",
    "downloads",
    "downloads.open",
    "webRequest",
    "webRequestBlocking",
    "storage"
  ],
  "background": {
    "page": "background.html"
  },
  "options_ui": {
    "page": "options/options.html",
    "browser_style": true
  }
}