Examine source code of versionshower

{
  "manifest_version": 2,
  "name": "versionshower",
  "version": "1.4resigned1",
  "description": "shows your current flashplayer- and the firefox version with one click",
  "icons": {
    "32": "icons/version-32.png"
  },
  "applications": {
    "gecko": {
      "id": "jid0-qmBgPmtVNOZZsQTshBgAlFDBmR4@jetpack",
      "strict_min_version": "45.0"
    }
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/version-32.png",
    "default_title": "versions",
    "default_popup": "popup/versions.html"
  },
  "content_security_policy": "script-src 'self'; object-src 'self'"
}