Examine source code of Domainswitcher

{
  "manifest_version": 2,
  "name": "Domainswitcher",
  "version": "1.2resigned1",
  "homepage_url": "https://github.com/peterbe/domainswitcher",
  "description": "Change domain, only.",
  "icons": {
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png"
  },
  "applications": {
    "gecko": {
      "id": "domainswitcher@peterbe.com",
      "strict_min_version": "45.0"
    }
  },
  "permissions": [
    "tabs"
  ],
  "page_action": {
    "default_icon": "icons/icon-32.png",
    "default_title": "Domainswitcher",
    "default_popup": "choose_domain.html"
  },
  "background": {
    "scripts": [
      "domainswitcher.js"
    ]
  }
}