Examine source code of Display Subtitle

{
  "manifest_version": 2,
  "name": "Display Subtitle",
  "version": "2.0",
  "description": "Display subtitle from external source",
  "homepage_url": "https://github.com/sauravshah31/Display_Subtitle",
  "icons": {
    "48": "assets/logo_48.png",
    "96": "assets/logo_96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_end",
      "js": [
        "src/SubtitleBox.js "
      ]
    }
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "48": "assets/logo_48.png",
      "96": "assets/logo_96.png"
    },
    "default_popup": "src/main.html",
    "default_title": "Display Subtitle"
  },
  "permissions": [
    "<all_urls>",
    "activeTab"
  ]
}