Examine source code of TextAreaExtention

{
  "manifest_version": 2,
  "name": "TextAreaExtention",
  "version": "1.0",
  "description": "Add the resize option in the textarea of sgs.",
  "icons": {
    "48": "TextAreaExtentionIcon48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "addResize.js"
      ],
      "all_frames": true,
      "run_at": "document_idle"
    }
  ],
  "applications": {
    "gecko": {
      "id": "@textareaextention"
    }
  }
}