Examine source code of Video Frame extractor

{
  "author": "DrewTW",
  "manifest_version": 2,
  "name": "Video Frame extractor",
  "version": "1.0",
  "description": "This extension will try extracting any video's frame as a full image",
  "browser_action": {
    "default_icon": {
      "32": "icons/32.png",
      "48": "icons/48.png",
      "64": "icons/64.png",
      "128": "icons/128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ]
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "VideoFrameExtract@DrewTW",
      "strict_min_version": "56.0"
    }
  }
}