Examine source code of CenterSVG

{
  "id": "jid0-jrE0BuiCBBYRzTc4SCO7JV1Vlz0",
  "description": "Adds a grey background to SVG files and centers them, just like normal images.",
  "manifest_version": 2,
  "name": "CenterSVG",
  "title": "CenterSVG",
  "author": "tobbi",
  "version": "1.1resigned1",
  "license": "MPL-2.0",
  "homepage_url": "http://www.tobbi.ml",
  "_icons": {
    "16": "data/icon16.png",
    "48": "data/icon48.png",
    "64": "data/icon64.png"
  },
  "_applications": {
    "gecko": {
      "id": "jid0-jrE0BuiCBBYRzTc4SCO7JV1Vlz0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*.svg"
      ],
      "js": [
        "data/centersvg.js"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": [
      "data/centersvg_background.js"
    ]
  },
  "_browser_action": {
    "default_icon": {
      "16": "data/icon16.png",
      "48": "data/icon48.png",
      "64": "data/icon64.png"
    }
  },
  "permissions": [
    "storage"
  ],
  "web_accessible_resources": [
    "data/styles.css"
  ],
  "options_ui": {
    "browser_style": true,
    "page": "options.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "jid0-jrE0BuiCBBYRzTc4SCO7JV1Vlz0@jetpack"
    }
  }
}