Examine source code of Relingo - Master words from any webpage

{
  "manifest_version": 2,
  "name": "__MSG_PKG_NAME__",
  "description": "__MSG_PKG_DESC__",
  "default_locale": "en",
  "version": "3.28.0",
  "permissions": [
    "storage",
    "cookies",
    "contextMenus",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "build/background.js"
    ]
  },
  "icons": {
    "16": "icons/icon-48.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "commands": {
    "toggleCurrentSite": {
      "suggested_key": {
        "default": "Alt+E",
        "mac": "MacCtrl+E"
      },
      "description": "__MSG_TOGGLE__"
    },
    "fullTextTranslate": {
      "suggested_key": {
        "default": "Alt+F",
        "mac": "MacCtrl+F"
      },
      "description": "__MSG_FULLTEXT_TRANSLATE__"
    },
    "openSettings": {
      "suggested_key": {
        "default": "Alt+S",
        "mac": "MacCtrl+S"
      },
      "description": "__MSG_OPEN_SETTING__"
    },
    "clickFloatBall": {
      "description": "__MSG_CLICK_FLOAT_BALL__"
    },
    "openCurrentWordslist": {
      "description": "__MSG_OPEN_CURRENT_WORDLIST__"
    },
    "addToReadLater": {
      "description": "__MSG_ADD_TO_READ_LATER__"
    },
    "toggleOnce": {
      "description": "__MSG_TOGGLE_ONCE__"
    },
    "toggleStar": {
      "description": "__MSG_TOGGLE_STAR__"
    },
    "toggleMaster": {
      "description": "__MSG_TOGGLE_MASTER__"
    },
    "toggleBilingualCaption": {
      "description": "__MSG_TOGGLE_BILINGUAL_CAPTION__"
    },
    "enterImmersiveVideo": {
      "description": "__MSG_ENTER_IMMERSIVE_VIDEO__"
    },
    "openQuickTranslate": {
      "description": "__MSG_OPEN_QUICK_TRANSLATE__"
    }
  },
  "host_permissions": [
    "*://*.relingo.net/",
    "http://localhost/*",
    "http://127.0.0.1/*",
    "*://*.localhost/*"
  ],
  "web_accessible_resources": [
    "*"
  ],
  "externally_connectable": {
    "matches": [
      "*://*.relingo.net/*"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*",
        "file://*/*"
      ],
      "js": [
        "build/content.js"
      ],
      "css": [
        "build/content.css"
      ],
      "run_at": "document_end",
      "all_frames": true
    },
    {
      "matches": [
        "https://youtube.com/*",
        "https://m.youtube.com/*",
        "https://www.youtube.com/*",
        "https://netflix.com/*",
        "https://www.netflix.com/*",
        "https://www.coursera.org/*",
        "https://coursera.org/*",
        "https://www.udemy.com/*",
        "https://udemy.com/*",
        "https://*.udemy.cn/*",
        "https://*.udemy.com/*",
        "https://*.ted.com/*",
        "https://*.youtube-nocookie.com/*",
        "https://*.max.com/*",
        "https://*.disneyplus.com/*",
        "https://*.edx.org/*",
        "https://*.bilibili.com/*",
        "https://hianimez.to/*",
        "https://megacloud.blog/*"
      ],
      "js": [
        "build/content_start.js"
      ],
      "run_at": "document_start",
      "css": [
        "build/content_start.css"
      ],
      "all_frames": true
    }
  ],
  "browser_action": {
    "default_title": "__MSG_PKG_NAME__"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{1a80c9a2-91e3-40a6-a259-140fc46151be}"
    },
    "gecko_android": {
      "id": "{1a80c9a2-91e3-40a6-a259-140fc46151be}"
    }
  }
}