Examine source code of CustomCSS Injector

{
  "manifest_version": 2,
  "name": "CustomCSS",
  "version": "1.3.2",
  "browser_specific_settings": {
    "gecko": {
      "id": "{b2c51689-0095-472b-b900-2b3911fd5089}"
    }
  },
  "description": "Write any CSS rules for any websites",
  "icons": {
    "48": "icons/CCSSI_icon_v2_48.png"
  },
  "permissions": [
    "storage",
    "<all_urls>",
    "contextMenus",
    "notifications"
  ],
  "browser_action": {
    "browser_style": true,
    "default_popup": "popup/popup.html",
    "default_icon": {
      "48": "icons/CCSSI_icon_v2_48.png",
      "96": "icons/CCSSI_icon_v2_96.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "customcss.js"
      ],
      "run_at": "document_start",
      "all_frames": true,
      "match_about_blank": true
    }
  ]
}