Examine source code of Hold It Sideways

{
  "manifest_version": 2,
  "version": "0.3.2resigned1",
  "name": "hold it sideways",
  "description": "Flip a manga/comic page with ',' and '.' and read inverted text like a human bean.",
  "developer": {
    "name": "kootoopas",
    "url": "https://github.com/kootoopas"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "match_about_blank": true,
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{1d394f40-e6eb-470d-9568-81ddad590fad}"
    }
  }
}